1 40 195 https://bereket-haileab.geology.sites.carleton.edu/files/original/c24e79b749a001892d830bd1dd5d80f2.jpeg 1b4dc3a892d695602334fd93553b6cba Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-8 Subject The topic of the resource Tuff Description An account of the resource Major Mineral: hornblende <br />Minor Mineral: clinopyroxene altering to chlorite, sanidine, titanite, sericite, calcite, apatite<br />Click <a href="https://www.digitalscope.org/ViewerUI/?SlideId=6ebde66b-c6cc-4d73-9f0d-d3b95ab923e9">here</a> for a high resolution scan<br /><br /> <p>BH250-8 is a strikingly beautiful tuff with rich mineralogical features. It contains basaltic hornblende—some crystals showing zoning—as well as both orthopyroxene (OPX) and clinopyroxene (CPX), with some CPX grains displaying anomalous interference colors. Scattered quartz grains are also present. Plagioclase feldspars exhibit alteration to sericite, while portions of the pyroxene have altered to chlorite. Accessory minerals include sphene (titanite) and exceptionally large, well-formed apatite grains—some cut parallel and others perpendicular to the c-axis, clearly revealing basal cleavage. Secondary calcite occurs along veins and voids, and the groundmass contains devitrified and recrystallized volcanic glass. This is a particularly beautiful and mineralogically diverse sample.<br /><br />There are several apatite crystals cut parallel to the C-axis that can be used to determine, length fast, length slow optical property as seeing in the video.</p> Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 8. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=a0a0bd40ee6449d08239c495b3b69bb1" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=a0a0bd40ee6449d08239c495b3b69bb1">here</a><a href="https://carleton.maps.arcgis.com/home/item.html?id=056af387bc7d45bfa762ccd20d45d96b"></a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1l1qnS723ph71--VAF8_tRN7Le8kF1tuk/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RLGeQ-VcaA7zH_smwNBkhCsStR0373xF/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/16yGJO2oSAeTCLLqrpCFhaXAqKyT2QPiY/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1AvJn02wCKcxl5B1SH2pDX0CbCUhdn8jo/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14ys7YVosrwZHm8btnye6V3icL0Yat75H/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1KFSPbximkQlk4u5dP6npU1vcpwNzmSMz/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1WShR3AY9pJWG9emTk9UJJ9wxRjBoBiUX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1GIwdoePJw8pxnya8ASrhnBiqGe8H-TgX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/16QhBGImpt3pfYPi4NncYW_s2_fKJGZC7/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_MRN8sEFPw-pKXoHYRjRxiI3CV0nQuDy/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1d4vuWNWZ0y9bJ-b8P4odEB8JdYlOekWI/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jKnVwGcI6KjmDOWoVWQZoJBEEKxN9U7H/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1mk0r0kcv46_RnyQn4f73Y3RdJIokn-TD/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Alteration (sericite Anomalous interference colors Apatite basalt Basaltic hornblende chlorite) Clinopyroxene (CPX) Devitrified Glass Hornblende igneous length fast length slow mafic Orthopyroxene (OPX) Recrystallization Titanite (Sphene) Titanoaugite tuff volcanic volcaniclastic welded tuff Zoned minerals https://bereket-haileab.geology.sites.carleton.edu/files/original/1e4f03f6a59fadb1775f2ca43d8f470a.jpg e16dafeae667600a4a87a17ed46fab94 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-9 Subject The topic of the resource Ortho-pyroxenite Description An account of the resource Major Minerals: orthopyroxene, Minor Minerals: clinopyroxene, olivine, oxides Texture: exsolution lamellae, solid solution between opx and cpx Physical property: 90 degrees cleavage, pyroxene cleavage Petrology: Pyroxenite is an ultramafic, igneous rock composed predominantly of pyroxene minerals, specifically orthopyroxene (opx) and clinopyroxene (cpx), often in nearly equal or varying proportions. In the Webster, North Carolina region, pyroxenites are typically associated with mafic-ultramafic intrusions. These rocks are believed to represent crystallized cumulates from high-temperature mafic magmas or solid residues from partial melting processes in the mantle. BH250-9 is an ortho-pyroxenite with enstatite being the dominant mineral and few olivine, oxides and the exsolved clino-pyrorxene as the makeup of the mineralogy of the rock. Texture: In the pyroxene of BH250-9, exsolution lamellae are common, especially in orthopyroxene, where thin blades of clinopyroxene exsolve due to cooling from high temperature solid solutions. The presence of solid solution between orthopyroxene and clinopyroxene indicates high-temperature equilibrium before exsolution, suggesting that the rock crystallized or equilibrated at elevated pressures and temperatures. Physical and Optical Properties: Cleavage at ~90° is characteristic of pyroxenes (two cleavages intersecting nearly at right angles). The pyroxenes may show parting, exsolution textures, and pleochroism in thin section, aiding in mineral identification. Orthopyroxene is usually brown to green in thin section; clinopyroxene can be colorless to pale green. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-9. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and handsample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=20a9374bea664d20954eab856a70e7f5" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=20a9374bea664d20954eab856a70e7f5">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Zh1ly4CUaS5loy9lXnWm5M-381mXuq-M/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/142OuOFGx65zCRWp1EfYob5qtHsoogr4_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1H2XDNs6qcVANB9_Io2lYHNgwFCXB7RiZ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1b6jtQXpVPesqQMyjPguyUtMCrdKw7okS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/17x5utBrUNk781qozoI_zMk5_c1Y8fT3l/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/17Rny7ew4cja_VfJqswhV3qyVh4mTd8Fc/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1AOQijCjgJe3kAP5PG6xmAlH_E9A6ZLMp/preview" allow="autoplay"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Webster, North Carolina, USA Creator An entity primarily responsible for making the resource Bereket Haileab Clinopyroxene Enstatite Exsolution Exsolution lamellae gabbro igneous mafic Mafic-ultramafic intrusion North Carolina Ortho-pyroxenite Orthopyroxene plutonic Pyroxene cleavage (90°) Pyroxene exsolution Pyroxenite cumulate Solid solution Solid solution (opx–cpx) Ultramafic rock Webster https://bereket-haileab.geology.sites.carleton.edu/files/original/721ee5d936a00f317f8a3fe6212eee36.jpg ba5b24e5a7e15a921b99071351b3e2bf Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-11 Subject The topic of the resource Gabbro Description An account of the resource Major Mineral: plagioclase, labradorite, orthopyroxne, clinopyroxene Minor Minerals: olivine, biotite Texture: euhedral plagioclase, anherdral pyroxenes, useful for two competent phase diagrams Optics: optic axis figure on labradorite Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 11. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=607b6049531e4e0d8ec22e53a6d7d4dd" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=607b6049531e4e0d8ec22e53a6d7d4dd">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/16Zgz9-szMKIdWal6wBAZl_taEXAFN-_m/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1UAbOX2xO65mT7Y7wBtnKmyQ464dWnYlO/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1HSCWMXbY5PoY3Au8EC6w1A3ocm4_IWre/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-G1zsBRxEDBUQbYPI0nAoGspUtL5UO2i/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/188xSQuZV2bWoTcLyCqODV1iII-At78-d/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/145JV5gkNnROLgWBvqjkwcXYooSUqdCvd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1UrXg2-cT706Cwc8_FcqO9FAJQEAi37cd/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab https://bereket-haileab.geology.sites.carleton.edu/files/original/3ca30622751c40964226d88303ce386c.jpeg 55bc810c63e9df93b6f7fe1f11d37cfe Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-13 Subject The topic of the resource Granite Description An account of the resource Major Minerals: quartz, orthoclase, albite Minor Minerals: hornblende, titanite (sphene), zircon, biotite, microcline, perthite, sericite, chlorite, calcite (secondary), apatite Mineralogy Comments: myrmekite Optics: small 2V, biotite BXA(x) figure, optically negative biaxial mineral, biotite cut perpendicular to c-axis, radiation damage, pleochroic halo, tar tarn twining Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-13. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=38b32e0ac84f4f36a530c2a339a45589" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=38ea461ce7b74f068953c9d1ee42644c">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1cJI7zDZY1RtFYwnCvcskmUgq0UhXe1-v/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IBGmc5XPJtFUdNPmfdonlh3z8SRAedi8/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/176KRF0_7WHLKpEBIy9Daeg3DrO8xjtdl/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OgGj5utm683ODh0HBzxrb0-IE0pYCG7T/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BtSJxKEZLVwTC9-SEreOowOhiMwbIx0U/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/161xK1tlJn7GbJwwfVZrxLZhoHK7kDzNn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Tj_dyB4yAnos0tGTvYUpa2pReIi3wPX8/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-yEkjWsGsZVEx-ijk7tJepkWY4w__cgD/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_JVcNKe6N8pNu-JQVnQzOg9sW4-RgYUi/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fbWntjGx7-Vi9OqkZbhvGr9NgHy6hwog/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ud1Ri0jIdfPg04odQwY3fCJ5euxU-uuv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19mDY_envJ5WlLSIC3tNE-XrmLN0F7YV4/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Contributor An entity responsible for making contributions to the resource Bereket Haileab felsic granite igneous plutonic https://bereket-haileab.geology.sites.carleton.edu/files/original/da98f6b873d85c5ec3a25358375f1225.jpeg df8533def48341d8a24862a55165e7b2 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-15 Subject The topic of the resource Andesite, true andesite Description An account of the resource Major Minerals: amphibole, plagioclase <br />Minor Mineral: glass <br />Texture: amphibole dehydration, trachytic flow<br /><br /> <p>BH250-15b is an andesite from Mt. Shasta, California. When plotted on the TAS (Total Alkali–Silica) diagram, it falls within the dacite field, indicating a slightly more evolved composition than typical andesite. Twinned amphiboles and plagioclase feldspar are common. Its mineralogy includes phenocrysts of hornblende and plagioclase feldspar. The matrix consists of fine-grained feldspar and volcanic glass. Both phenocryst types exhibit zoning, suggesting changes in magmatic conditions during crystallization. The hornblende phenocrysts display dehydration reaction rims, with the extent of alteration ranging from thin margins to rims so extensive that they have nearly consumed the amphibole entirely.<br /><br /></p> <p><span style="color: black;">In this sample, you can observe<span class="apple-converted-space">&nbsp;</span><strong data-start="120" data-end="146"><span style="font-weight: normal;">hornblende dehydration</span></strong><b>,</b> a key mineral reaction that records changing magma conditions during ascent. Hornblende is a hydrous amphibole, stable only at relatively high pressure and in water-rich magmas. As magma rises, pressure decreases and dissolved water exsolves, destabilizing hornblende. It then breaks down into minerals stable under drier, lower-pressure conditions, typically forming pyroxene, plagioclase, and iron oxides such as magnetite, while releasing water vapor.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="604" data-end="1212"><span style="color: black;">This process commonly produces<span class="apple-converted-space">&nbsp;</span><strong data-start="635" data-end="652"><span style="font-weight: normal;">reaction rims</span></strong><span class="apple-converted-space">&nbsp;</span>around hornblende crystals. These dark, opaque “opacite rims” consist of very fine-grained oxides and pyroxenes and indicate that the dehydration reaction began but did not go to completion, usually due to relatively rapid magma ascent. In contrast, complete alteration occurs when hornblende is entirely replaced by these secondary minerals, preserving only the original crystal shape as a<span class="apple-converted-space">&nbsp;</span><strong data-start="1044" data-end="1059"><span style="font-weight: normal;">pseudomorph</span></strong>. In some cases, the breakdown products may also include minor glass or extremely fine-grained intergrowths, reflecting rapid quenching near the surface.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="1214" data-end="1671"><span style="color: black;">The thickness and development of these rims provide important clues about magma dynamics. Thin rims suggest rapid ascent and limited time for reaction, whereas thick rims or complete replacement indicate slower ascent, longer residence at shallow depth, or more extensive degassing prior to eruption. These textures are therefore considered classic<span class="apple-converted-space">&nbsp;</span><strong data-start="1563" data-end="1590"><span style="font-weight: normal;">disequilibrium features</span></strong>, showing that minerals did not have time to fully adjust to changing conditions.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="1673" data-end="2187"><strong data-start="1673" data-end="1821"><span style="color: black; font-weight: normal;">Compared to BH250-15b and BH250-120, where most of the hornblende is completely dehydrated and replaced, this sample preserves earlier stages of the reaction.</span></strong><span class="apple-converted-space"><span style="color: black;">&nbsp;</span></span><span style="color: black;">The presence of partial reaction rims here suggests that magma ascent was faster or that the crystals experienced less time under low-pressure, degassing conditions. In contrast, the more complete dehydration observed in BH250-120 indicates longer residence at shallow depths or more extensive pre-eruptive degassing, allowing the reaction to proceed to completion.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="2189" data-end="2640" data-is-last-node="" data-is-only-node=""><span style="color: black;">Overall, hornblende dehydration textures are powerful indicators of magma evolution. Because hornblende stability is strongly tied to water content, its breakdown provides direct evidence of<span class="apple-converted-space">&nbsp;</span><strong data-start="2380" data-end="2424"><span style="font-weight: normal;">pre-eruptive degassing and decompression</span></strong><span class="apple-converted-space">&nbsp;</span>in volcanic systems. These features are especially common in intermediate magmas such as andesite and dacite and are widely used to interpret ascent rates, storage conditions, and eruption dynamics in volcanic arcs.</span></p> <br /><br />Optics: pleochroism in amphibole, Carlsbad twining Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-15. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=87cb287111644d20a3e727d83a795ebd" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe> <a href="&lt;iframe src=&quot;https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=87cb287111644d20a3e727d83a795ebd&quot; width=&quot;400&quot; height=&quot;600&quot; frameborder=&quot;0&quot; style=&quot;border:0&quot; allowfullscreen&gt;iFrames are not supported on this page.&lt;/iframe&gt;"></a><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=1556b48fc03540b8ada472f0d3898607">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PH1WZBRbYyGwWIIVKjTXjty3EuuyPYZv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15C51AErjn3uuvHFr43n4LlT_sE05W3TY/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1liRBBlmDfx2Kz1O2zH_6RdDuKVrktIGP/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lECGx-VS8E82aLsboB-AlvPzttCZvYIV/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wRtiI5ouH9z13twFZvMcKVCOGC4onQ_G/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1akJjToYhi_k7g7O05-WDpl7yyvpin-Rv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1O1wubeYi99yo0HLadOHFCF5X0B8hqCme/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1691cxuMO9uSKM-OkM45r7EA0t7f8j2Ad/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1g3MpeQE7MgLR5Ao86WOhdWySOmXA0pFn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15YS5CGEvCiUWUzhNzO4Hv9A0PCEa6Lw9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1olveWFKtwgPe4XEhcmEwVZvMoA_cGk_N/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QGSnmx5dbGrd-sDD9tnz5kdZB11Qqzw7/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/12KSdFWvzb1j86AQDcCylAtr4zILSriR_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1KAWsU-CLwiFFVNvaohn9IQ5ePgGwqT5P/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Contributor An entity responsible for making contributions to the resource Bereket Haileab andesite dacite Dehydration reaction in amphiboles Dehydration Rim felsic Hornblende igneous intermediate Mt Shasta phenocryst Plagioclase TagsAmphibole Alteration TAS diagram Total Alkali–Silica diagram volcanic Volcanic glass Zoning https://bereket-haileab.geology.sites.carleton.edu/files/original/3c96c75955f18fe1d92798a0aff66b28.jpg de96be70c9934138a0e34f88d96dc416 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-15b Subject The topic of the resource Andesite Description An account of the resource Major Minerals: amphibole, plagioclase<br />Minor minerals: glass<br />Texture: trachytic flow, dehydration rim on amphibole<br /><br /> <p>BH250-15b is an andesite from Mt. Shasta, California. When plotted on the TAS (Total Alkali–Silica) diagram, it falls within the dacite field, indicating a slightly more evolved composition than typical andesite. Twinned amphiboles and plagioclase feldspar are common. Its mineralogy includes phenocrysts of hornblende and plagioclase feldspar. The matrix consists of fine-grained feldspar and volcanic glass. Both phenocryst types exhibit zoning, suggesting changes in magmatic conditions during crystallization. The hornblende phenocrysts display dehydration reaction rims, with the extent of alteration ranging from thin margins to rims so extensive that they have nearly consumed the amphibole entirely.<br /><br /></p> <p><span style="color: black;">In this sample, you can observe<span class="apple-converted-space">&nbsp;</span><strong data-start="120" data-end="146"><span style="font-weight: normal;">hornblende dehydration</span></strong><b>,</b> a key mineral reaction that records changing magma conditions during ascent. Hornblende is a hydrous amphibole, stable only at relatively high pressure and in water-rich magmas. As magma rises, pressure decreases and dissolved water exsolves, destabilizing hornblende. It then breaks down into minerals stable under drier, lower-pressure conditions, typically forming pyroxene, plagioclase, and iron oxides such as magnetite, while releasing water vapor.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="604" data-end="1212"><span style="color: black;">This process commonly produces<span class="apple-converted-space">&nbsp;</span><strong data-start="635" data-end="652"><span style="font-weight: normal;">reaction rims</span></strong><span class="apple-converted-space">&nbsp;</span>around hornblende crystals. These dark, opaque “opacite rims” consist of very fine-grained oxides and pyroxenes and indicate that the dehydration reaction began but did not go to completion, usually due to relatively rapid magma ascent. In contrast, complete alteration occurs when hornblende is entirely replaced by these secondary minerals, preserving only the original crystal shape as a<span class="apple-converted-space">&nbsp;</span><strong data-start="1044" data-end="1059"><span style="font-weight: normal;">pseudomorph</span></strong>. In some cases, the breakdown products may also include minor glass or extremely fine-grained intergrowths, reflecting rapid quenching near the surface.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="1214" data-end="1671"><span style="color: black;">The thickness and development of these rims provide important clues about magma dynamics. Thin rims suggest rapid ascent and limited time for reaction, whereas thick rims or complete replacement indicate slower ascent, longer residence at shallow depth, or more extensive degassing prior to eruption. These textures are therefore considered classic<span class="apple-converted-space">&nbsp;</span><strong data-start="1563" data-end="1590"><span style="font-weight: normal;">disequilibrium features</span></strong>, showing that minerals did not have time to fully adjust to changing conditions.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="1673" data-end="2187"><strong data-start="1673" data-end="1821"><span style="color: black; font-weight: normal;">Compared to BH250-120, where most of the hornblende is completely dehydrated and replaced, this sample preserves earlier stages of the reaction.</span></strong><span class="apple-converted-space"><span style="color: black;">&nbsp;</span></span><span style="color: black;">The presence of partial reaction rims here suggests that magma ascent was faster or that the crystals experienced less time under low-pressure, degassing conditions. In contrast, the more complete dehydration observed in BH250-120 indicates longer residence at shallow depths or more extensive pre-eruptive degassing, allowing the reaction to proceed to completion.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="2189" data-end="2640" data-is-last-node="" data-is-only-node=""><span style="color: black;">Overall, hornblende dehydration textures are powerful indicators of magma evolution. Because hornblende stability is strongly tied to water content, its breakdown provides direct evidence of<span class="apple-converted-space">&nbsp;</span><strong data-start="2380" data-end="2424"><span style="font-weight: normal;">pre-eruptive degassing and decompression</span></strong><span class="apple-converted-space">&nbsp;</span>in volcanic systems. These features are especially common in intermediate magmas such as andesite and dacite and are widely used to interpret ascent rates, storage conditions, and eruption dynamics in volcanic arcs.<o:p></o:p></span></p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1910588120&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Mt. Shasta, California, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 15b. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=0189377d17504a34af71bbc3099602e3" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe> &nbsp;<br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=5075f33fcb6249a8b7b0a98e47f54791">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1C3mZOUJ5jOAUOvXLHzSbT-crRyiVkXoA/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FK_Oxli2AxlauCyOWTznGoaod_zwhwS1/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1WjZI8mUuWnB4aeUPj6VHFeTI-qCtSJKT/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1n5jZoCjYCUWhw3VwrZRxOJEP0F1FOiwN/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/18RJUQNSKqlA2s7mh-X6MVb-6o0ghct06/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1EiBtxs6sCFJeHMG8R6AYyAwBdZTK8D-d/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1O9OB8JmpXWsj6EYy59THjjO_EGPfaP0v/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1o8rbSoUyDTC709WpJh4VeAOkYmM9XI2L/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1HkAZJEbA4SnnOMC9l4-ah4Y1_9lR3Ysv/preview" allow="autoplay"></iframe> TAS diagram for sample 15b. Creator An entity primarily responsible for making the resource Bereket Haileab Amphibole Alteration andesite dacite Dehydration reaction in amphiboles Dehydration Rim felsic Hornblende igneous Mt Shasta phenocryst Plagioclase TAS diagram Total Alkali–Silica diagram volcanic Volcanic glass Zoning https://bereket-haileab.geology.sites.carleton.edu/files/original/20774fd1684e8c4f9fe3d05f7e6044a3.jpg 4745151a71ea8615af7d216527bffe60 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-16 Subject The topic of the resource Phonolite Description An account of the resource Major Minerals: orthoclase, nepheline, aegirine-augite, albite, cordierite Minor Minerals: titanite (sphene), biotite, hornblende, apatite, anthophyllite, muscovite Mineralogy Comments: hornblende euhedral Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 16. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=365d00f450f341de99126330d3a3d933" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=365d00f450f341de99126330d3a3d933">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1HHOXXvtn2W8-Dq9yVlW8Gfn-y8QKBgjq/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1A07cRQZc94JIfRSIG3kEXW5-P31eNxvA/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xj908k9MxxtiXlqQke311LEKqzxQUq_3/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pyX4g15BA80YCZugTzrSmQ5lI9c4sfTt/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1vE8hFzm0dXAEEVnD8D75Esty63WSihKt/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PFz8usQYGHEHkmRMgeJnUzYUu04eGVBF/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lKcrHVKpKn4Xhlo-K6PUdpOFVoJBhxYI/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1NX0Z1bbTuzOgKD6jZ8lfXSwkN6CWjaDz/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Fl3oWoPb7sWYish4XxGtcFy2mMibCS4c/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab igneous intermediate phonolite volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/73298495cf39fd0c53c08214852851a9.jpg 416310617c73dca607bc2bbbe78823ef Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-17 Subject The topic of the resource Dunite Description An account of the resource Major Mineral: olivine Minor Minerals: clinopyroxene, magnetite, serpentine Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 17. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=a8b5ce98f4754c96a108e7e7e56d416a" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=a8b5ce98f4754c96a108e7e7e56d416a">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Q79K2qLhYzXO56VtEMe7WQuystwzF9WA/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/152DZ_0fV7RdJPJXY6Qum9PRg7YkcShUj/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XJ2zctadXHWYX7okQ4B1brDBl0hm95Zy/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab dunite igneous plutonic ultramafic https://bereket-haileab.geology.sites.carleton.edu/files/original/48fafb17db021c0262ea002c2b627d54.jpg b153d7c4311544dd9e5b68bcc65f60c1 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-18b Subject The topic of the resource Gabbro Description An account of the resource Major Minerals: spinel, clinopyroxene, olivine Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Utah, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 18b. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Creator An entity primarily responsible for making the resource Bereket Haileab Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=202f09ae437c48f0805a0acbbc501abb" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe> <br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=91cdd9d370a849f081326e76ad8796b4">here</a> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ejdZ0_ZfRz3S4NF2V41I7P9P8I9Z4rIv/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1viMl6U2yO3m-8-e9ZMhQmAWrClocvDDW/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1A5FvtbibXRd4V6MnaXlmoFSEOnuKikWh/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1sTWfUScdPxK9AJ2EtplHRYeMZJGV_6f5/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fAuLcV61OmR_VR7shHmXb6vXooRwRJZw/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kiNuSoHTjLxNb-gfgjfDtz5y4WMgOkav/preview" allow="autoplay"></iframe> gabbro igneous mafic plutonic https://bereket-haileab.geology.sites.carleton.edu/files/original/af3fbe720df930760777da7ef6da35e8.jpg 1173545ed8f4e4cb60d9a76190786b69 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-19 Subject The topic of the resource Tuff, Welded tuff, Ignimbrite Description An account of the resource Major Minerals: quartz, albite, biotite, sanidine, glass, basaltic hornblende, clinopyroxene, augite<br />Mineralogy Comment: biotite shows kink band, possibly deformation during flow; perfect cleavage is visible in the biotite, zoning&nbsp;<br /><br /> <p>BH250-19 is a welded tuff containing phenocrysts of basaltic hornblende, biotite, clinopyroxene, orthopyroxene, and quartz. The matrix is composed of devitrified volcanic glass, preserving the texture typical of welded pyroclastic deposits. This thin section is an excellent teaching example for identifying welded tuff textures, recognizing phenocrysts, and distinguishing between biotite and hornblende under the microscope. Evidence of brecciation is also present, giving the rock characteristics of a volcanic breccia. When plotted on the TAS (Total Alkali–Silica) diagram, the bulk composition falls at the boundary between andesite and trachyandesite, reflecting a transitional composition in the volcanic series.</p> <br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1158317021&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 19. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=51a58c15b64f46f69a6de7b2174a919d" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=51a58c15b64f46f69a6de7b2174a919d">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1d0agziKHCM3w3h7-Jq-oJsJijDBYUk-a/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1AJ3C1I9ipurdxMUJcD4BetxMOXGy16jG/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1u3ffFLpp4LagAHmDSlECXTTgYG8Obl2B/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lgfrtESBOS_0j9uT1wgFfzg6Z9VxBHlr/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1YRoG_Dopm5GXd-ogF1MHgPzc25EZhYJR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1n3TjSnoAH9fyuTnpjmHM_oQVgzXeCYEK/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1EtKaShXXEc4s8iPQFQ6NpyL1qf6niosV/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JwXoszulF7k4mnoYpbCrRToCf2eJ4oA2/preview" allow="autoplay"><iframe src="https://drive.google.com/file/d/1fZSwqrXdc4TzsfFB3qG-Qzsae2xGMLje/preview" width="100%" height="480" allow="autoplay"></iframe></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1G8kJObVOdTxhQn45xPnS5GgYKokTkN-Q/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1NFC5NmX702TjHp5vv5MePicRYF4hl-ep/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gq_9fFEaFAfZqjB7qBS_UgD2NfaWfqkN/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-19. Creator An entity primarily responsible for making the resource Bereket Haileab andesite Basaltic hornblende Biotite Brecciation Clinopyroxene Devitrified Glass Hornblende Orthopyroxene phenocryst Quartz sedimentary TAS diagram Total Alkali Silica diagram Trachyandesite tuff volcanic Volcanic Breccia volcaniclastic welded tuff https://bereket-haileab.geology.sites.carleton.edu/files/original/31a940983936e3d66c18be4aa392d23c.jpg 297bff63d0bdbdcf565e76d5b658944a Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-24 Subject The topic of the resource Hornblende Gabbro Description An account of the resource Major Minerals: hornblende, plagioclase, hypersthene, biotite, enstatite Minor Minerals: iron-titanium oxide Mineralogy Comments: hornblende showing perfect two cleavages, 60/120 degrees cleavage Hornblende gabbro is a mafic rock, compositionally similar to gabbro. Hornblende-bearing gabbros are indicative of hydrous, calc-alkaline magmatism typically associated with convergent-margin (arc) environments. Amphibole-rich gabbros often crystallize from water saturated basaltic magmas derived from above a subduction zone. This thin section features some of the most beautiful hornblende and biotite crystals observed so far. Both minerals are cut in various orientations, displaying hornblende's two cleavages at ~60°/120° and biotite's single perfect cleavage. Some biotite grains are oriented perpendicular to the c-axis, and thus lack visible cleavage. Both hornblende and biotite exhibit strong pleochroism, often occur intergrown, and can be easily mistaken for one another by students new to optical mineralogy. Numerous hypersthene (POX) grains are also present, showing either one or two cleavages depending on the cut. Hypersthene displays weak pleochroism. The plagioclase feldspar and associated mafic minerals are predominantly anhedral, suggesting near-simultaneous crystallization under similar temperature conditions. Iron-titanium oxides are abundant and evenly distributed throughout the thin section. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-24. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=bdebcb48111f4ad5a2ede3ecc4aaa4ba" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=bdebcb48111f4ad5a2ede3ecc4aaa4ba">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/13ED1Kk6eEBqWqB_9V7xWTVwJDIzZDFhs/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1HwgstfqldqX0PQM9jBRZo9BAjkNucAZ4/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1TU-iiY7lWHAW3o4ZwepslC1nQaezkAMg/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/198As53GxWv90GUhlEQI0kHUYVJ8g4LPG/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab amphibole cleavage Amphibole-rich Gabbro Biotite Biotite Cleavage Calc-alkaline Gabbro Cleavage Angles (Hornblende 60/120°) Cleavage in Thin Section Enstatite gabbro Hornblende Hornblende gabbro Hydrous Magmatism Hypersthene igneous Iron-Titanium Oxides mafic Pleochroic Minerals Pleochroism plutonic https://bereket-haileab.geology.sites.carleton.edu/files/original/df9ac4f2a41ef384b320088c4a6c7cce.jpg 25a83a661abd93f49cf0101b32815b08 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-33 Subject The topic of the resource Sodalite Description An account of the resource Major Mineral: Sodalite Minor Minerals: Oxides BH250-33 is a rock full of Sodalite minerals. Optical Character: Sodalite is isotropic, belonging to the cubic crystal system. Under plane-polarized light (PPL), it typically appears blue with low relief and generally shows no birefringence. It may exhibit a faint bluish tint in PPL, but remains isotropic under cross-polarized light. General Information: Sodalite is a relatively rare, blue-colored tectosilicate mineral within the feldspathoid group. It commonly forms in silica-undersaturated, alkaline igneous rocks such as nephelinite, phonolite, and sodalite syenite. Sodalite typically occurs in environments where quartz is absent or very scarce and is often associated with other feldspathoids like nepheline, leucite, cancrinite, and also with feldspar. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-33. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=d6eca2a9e14b4c8a90b1eb9871b4d045" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=d6eca2a9e14b4c8a90b1eb9871b4d045">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hZbzDSmWeIb1a_H6IC64gr6oO1mb8Bkp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1y5bcKqtTXuVP0mURwltZiwRaucSjCG3M/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1P0T6P95gEeeEmvGw8Hmmd1AN7Q_e3_z8/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1YkVyhsjPcALqLWqZoWK1bVnVmhFrcDPC/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Alkaline igneous rock Blue under PPL Feldspathoid igneous Isotropic mineral Low relief mafic phonolite plutonic Silica-undersaturated rock Sodalite Sodalite syenite https://bereket-haileab.geology.sites.carleton.edu/files/original/b165dd5f2e63f575257813b1e70d62d8.jpg 3f1cfbf1e23be18dd16023bb8867004a https://bereket-haileab.geology.sites.carleton.edu/files/original/2c4d90ee62c7128f26c3ae35a0434190.jpg 55591d9c5a5a795b71192539e8ea7a50 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-41 Subject The topic of the resource Dunite Description An account of the resource Major Mineral: forsterite, olivine<br />Minor Minerals: serpentine, magnetite<br />Texture: equigranular olivine<br /><br /> <p>BH250-41 is a dunite from<span>&nbsp;</span><span>Balsam</span>, composed almost entirely of forsterite-rich<span>&nbsp;</span><span>Olivine</span>. It is one of the most visually striking rocks, both in hand sample and especially in thin section. Under crossed polars, the olivine grains display vivid second-order interference colors. Well-oriented grains cut perpendicular to the c-axis yield excellent biaxial interference figures, with a 2V angle close to 90°, making the mineral appear nearly optically neutral. In this orientation, the isogyre forms a straight line that rotates smoothly about the optic axis—an ideal demonstration for teaching optical mineralogy.</p> <p data-start="674" data-end="1214">On the Olivine–Orthopyroxene–Clinopyroxene (Ol–Opx–Cpx) ternary diagram used for ultramafic igneous rock classification, dunite plots near the olivine apex because it contains more than 90% olivine, with only minor pyroxene if present. BH250-41 would therefore plot very close to the Ol corner of the diagram, firmly within the dunite field. This position reflects its highly magnesium-rich, mantle-derived composition and distinguishes it from harzburgite, lherzolite, and pyroxenite fields that contain greater proportions of pyroxenes.</p> <p data-start="1216" data-end="1664">Optically, olivine exhibits strong birefringence, producing bright second-order rainbow-like interference colors. It is biaxial with a 2V angle of approximately 90°, and in favorable orientations may appear nearly optically neutral. This sample provides excellent teaching examples for selecting grains that produce an optic-axis interference figure and for demonstrating the difference between biaxial and uniaxial behavior under the microscope.</p> <p data-start="1666" data-end="2191">BH250-41 also shows evidence in some thin sections of later metamorphic or alteration reactions, where primary olivine has begun to break down along fractures or grain margins. Common reactions include hydration to<span>&nbsp;</span><span>Serpentine</span><span>&nbsp;</span>or talc-bearing assemblages, recording fluid infiltration after crystallization. These secondary textures provide an excellent contrast between pristine mantle olivine and later alteration during tectonic uplift and weathering. A simplified serpentinization reaction is:</p> <span class="base"><span class="strut"></span><span class="mord">3(</span><span class="mspace"></span><span class="mord"><span class="mord text">MgFe)</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mord"><span class="mord text">SiO</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">4</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mspace">&nbsp;</span><span class="mopen">(</span><span class="mord text"><span class="mord">forsterite</span></span><span class="mclose">) </span><span class="mspace"></span><span class="mbin">+ 2</span><span class="mspace"></span></span><span class="base"><span class="strut"></span><span class="mord"><span class="mord text">H</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mord text"><span class="mord">O </span></span><span class="mspace"></span><span class="mbin">+ 2</span><span class="mspace"></span></span><span class="base"><span class="strut"></span><span class="mord"><span class="mord text">O</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2 </span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mspace"></span><span class="mrel">→ </span><span class="mspace"></span></span><span class="base"><span class="strut"></span><span class="mord">2</span><span class="mspace"></span><span class="mord"><span class="mord text">Mg</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mord"><span class="mord text">Si</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mord"><span class="mord text">O</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">5</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mopen">(</span><span class="mord text"><span class="mord">OH</span></span><span class="mclose">)<span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">4</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mspace">&nbsp;</span><span class="mopen">(</span><span class="mord text"><span class="mord">serpentine</span></span><span class="mclose">) </span><span class="mspace"></span><span class="mbin">+ </span><span class="mspace"></span></span><span class="base"><span class="strut"></span><span class="mord"><span class="mord text">Fe</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mord"><span class="mord text">O</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist"><span><span class="pstrut"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">4</span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist"><span></span></span></span></span></span></span><span class="mspace">&nbsp;</span><span class="mopen">(</span><span class="mord text"><span class="mord">magnetite</span></span><span class="mclose">)<br /><br /></span></span><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=981347482&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-41. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=426a8f55a4dd483ca317808ef82f20b1" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=426a8f55a4dd483ca317808ef82f20b1">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jl-5KZUFAbm3UuhI4czX0CYXcsifXOx_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XNRniVB7aQWWoA32Awlp84vfqnY4pQjf/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JxfcXWHXAREtxcQbCNqg2jwhizTYm1gS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-kPFzgN1RKuRHHMx5zRVGLUSgrgEkpZ9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1TMNilt8f60JiiP_3EX-Dv4xx1iqjWLqZ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bjNP6Carp4RV_n0Oa4LwSaLjgoXAJyHQ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1SSMdVlf18yv7Ym6pMgNjbcEWnzivo9ls/preview" allow="autoplay"><iframe width="100%" height="480" src="https://drive.google.com/file/d/16puBbmOxWiVoP3uob8vl77dopCZMb-TN/preview" allow="autoplay"></iframe></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hAKVyzvfRGUrVR48Gz_x8tlaJhnA22e2/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19de2VzZluIHRhS1XeGj1o698koJ1a54B/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1HGpg9JcT-Yw95b5cSDeZKxw6cpXmymYI/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/11TP06iGOAdc7PzLO_fcPOsIGu86wDL1k/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pRgBMlIT55SDEiEBJsTN_J3uxKULfKOZ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/18RkeyPoKqbBhrd9xUctkuQyMvWJgiyCe/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ecsjbkhjcqomvTr9iMPHCABFNW65KHR6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1TFMweiUFlfx_CZdr5konqpY3688xrU0R/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1NKZYYB89d5aDJXEw2IHZCQiprJyzeJCz/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FRACWu5QIyv1cTH6sRVVwMcj3W2S-k7k/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RvzxN4kC6bCy5rj0GR7W0Y0vy1fXgaAl/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kHxXUzDP6nQgZd82XaIicz3EUJ_KH_Z6/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/16puBbmOxWiVoP3uob8vl77dopCZMb-TN/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Balsam, North Carolina, USA 2V ~90° 2V angle 2V measurements Balsam Balsam NC biaxial Biaxial Mineral biaxial neutral cumulate cumulate rock dunite equigranular euhedral Fo-rich olivine forsterite granular texture high relief igneous igneous rock classification Interference Colors interference figure Isogyre Magnetite mantle derived mantle rock mantle xenolith mantle-derived magma Mg rich olivine North Carolina Ol-Opx-Cpx classification olivine olivine peridotite olivine-rich rock optic axis figure optically neutral orientation peridotite peridotite suite plutonic Serpentine Serpentinization talc alteration ultrabasic ultramafic Ultramafic rock upper mantle USA https://bereket-haileab.geology.sites.carleton.edu/files/original/c771a304248eabd7f6bb88ec0cbc54cc.jpg fef77f021089d880e6b149d7ce91ddd6 https://bereket-haileab.geology.sites.carleton.edu/files/original/52e1f6f2c2accfb84d6eba090e2634e5.jpg 1f372be2582a182478baea73d17f9b79 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-46 Subject The topic of the resource Anorthosite Description An account of the resource Major Mineral: anorthite <br />Minor Minerals: plagioclase, sericite <br />Mineralogy Comments: Carlsbad twinning, sericite secondary alteration<br /><br /> <p data-start="63" data-end="612">BH250-46 is an anorthosite sample from near Silver Bay, Minnesota, and is part of the Duluth Complex, a massive Mesoproterozoic-age intrusive body. Like other anorthosites in the complex, this rock is notable for its plagioclase-rich composition. The dominant mineral is plagioclase feldspar, typically ranging from labradorite to bytownite (An₅₀–An₈₀), comprising over 90% of the rock. Plagioclase crystals are generally euhedral to subhedral, often centimeter-scale, and exhibit weak to moderate zoning.</p> <p data-start="614" data-end="856">The bulk composition is high in Al₂O₃ due to plagioclase dominance, and low in SiO₂ compared to granitic rocks (typically ~50–55 wt%). K₂O and Na₂O contents are also low, consistent with the presence of calcic plagioclase.</p> <p data-start="858" data-end="1066">The rock exhibits a typical cumulate texture, and is found interlayered with troctolite, gabbro, and oxide-rich layers, appearing here as a large xenolith, as shown in the accompanying photograph.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1651630745&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 46. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=feb6f87a863a4bc885e06b92fa3ab4bf" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=feb6f87a863a4bc885e06b92fa3ab4bf">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1nwh4VWdjLRp7AVKJA4kUs-ZaDqLGq1fx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1A9S0sheLTdsVMZtARrKI3Sn1y3KAe3Vw/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XDA1QDblEi9QVC6iiQ_N3KuFv1KSIjxJ/preview" allow="autoplay"><iframe src="https://drive.google.com/file/d/19YF8ebU6iXPDhQVpED7HfoRAaWV52p2H/preview" width="100%" height="480" allow="autoplay"></iframe></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/116r1W5GlVGRTmi8TtC6mlw2pK6UMH3fu/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ixuqyqZn3uZvI_IKhawxZo8b07jycNBD/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BN9G7Z-YkrrWAgjOuF59hIt41-rgiqdX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1KlWoEG3O-Mf9DcUA65AKAkaqSQVOhWml/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Dz9byF9LID55W7H5wXcCZ4fW7HbtluOo/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1DlneqyLzLf3w56gQpw80S6YiQJ6e5NZQ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Mu6fXQ3gRqRDrFkjhtJ18wDgXWMYCtWh/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gb_4WGklPfYUEnIMnf2YACSbLC3THd3t/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-46. <iframe width="100%" height="480" src="https://drive.google.com/file/d/19YF8ebU6iXPDhQVpED7HfoRAaWV52p2H/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Silver Bay, Minnesota GPS coordinates: 47°17'20.07"N, 91°15'48.95"W Anorthite anorthosite cumulate rock Cumulate texture Duluth Complex euhedral plagioclase igneous Layered mafic intrusion mafic Mafic Intrusive Rock Midcontinent Rift Minnesota Northern Minnesota Plagioclase feldspar plutonic Silver Bay xenolith https://bereket-haileab.geology.sites.carleton.edu/files/original/c0aa0a1c62c2d9ed1d45d7aa494985bf.jpg 61fef343c2627c65e1afd5f254611ec1 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-46b Subject The topic of the resource Anorthosite Description An account of the resource Major Mineral: anorthite For more description, see BH250-46. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 46b. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=153379fed2814bb49071e717b043a421" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=153379fed2814bb49071e717b043a421">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BZBU71bOpwtwB2geNFzYKBobs158DPc5/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1L7XDARh7fwgIUWUAiiJ-3R0ItDeP-oqk/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-rb9hUMXzl1af5mcRtMvArYwI2jJYMMl/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gY92_SthzHpsxUvO7MaJZhGXh7xbxYiD/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1iEXQaWW_yT-oMnXcScuKbuVp_0ZfIihR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hf8NuF-hV_yZfllPzuGeOYQMtbWJnobs/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab anorthosite igneous mafic plutonic https://bereket-haileab.geology.sites.carleton.edu/files/original/f36508747e6965231206f720db9087c1.jpg 7b44a83a86a9c99b9974487424d36366 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-46c Subject The topic of the resource Anorthosite Description An account of the resource Major Mineral: anorthite For more description see BH250-46 Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 46c. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Creator An entity primarily responsible for making the resource Bereket Haileab Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=81f812b6f6e346eabe66faec5670eb91" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=81f812b6f6e346eabe66faec5670eb91">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1A_Wgq2jAnP8d8DLGSEjDD8pJ0kZmJqTv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1eJk5vs5ZKLMHYsZ-1zvmbMtiAVpkp5hS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1nPZKmRYXweBRxZad_8VAK-fM7e9cD6Ii/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15Jtr31Z-DjCmCDtGRlggQBG6b_EuVqqo/preview" allow="autoplay"></iframe> anorthosite igneous mafic plutonic https://bereket-haileab.geology.sites.carleton.edu/files/original/de06f0ce413b6060b294932a07387854.jpg c04779b2f01e486c71823f7f1f023410 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-49 Subject The topic of the resource Sacred Heart Granite Description An account of the resource Major Minerals: microcline, orthoclase, quartz <br />Minor Minerals: albite, biotite, muscovite, chlorite (pennite), sphene (titanite), zicon, monazite, oxides<br /><br />Mineralogy Comments: thin sections contain myrmekite<br />Alteration: orthoclase and plagicalse are altered to sercite (white mica), biotite to chlorie alteration<br /><br />BH250-49 is from the Sacred Heart Granite near Belview, Minnesota—one of our regular stops on field trips to the Minnesota River Valley. The Sacred Heart Granite is a Neoarchean pluton that intruded the older Morton and Montevideo gneiss complexes around 2.604 Ga (2,604 million years ago). Recenlty Emma Watson a Carleton College student from the Class of 2023, worked on this rock and obtained revised age determinations for the pluton.<br /><br />The intrusion represents the final phase of high-grade metamorphic and deformational events that produced the Morton Gneiss and surrounding metamorphic rocks, closely tied to the last stages of Neoarchean convergent tectonics in the region.<br /><br />BH250-49 is a medium-grained, massive, and typically pink to gray granite, generally fresh and only weakly deformed relative to the surrounding gneisses. Its modal composition is approximately 40% K-feldspar, 30% oligoclase (a plagioclase feldspar), and 25% quartz, with subordinate amounts of biotite.<br /><br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=861277415&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: near Sacred Heart, Minnesota, USA GPS Coordinates: 44°39'28.95"N, 95°20'17.19"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-49. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=d15b9b9ff56343b2a7f7fb383389579b" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=d15b9b9ff56343b2a7f7fb383389579b">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xV9z6lt_GaXvxOhVhKLsrLJeM9sx8kAb/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1HHxB1Kf8w7AokVk0q0W42MHQ03v8epLM/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1mAUsGHUCPcwVMSEBJgLyMn1lWp6ClTci/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1X8sdx-v5spXwu-54zOyaw_OF-6UNuDa5/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IPz1fSoJK5xSSrQ8TScgUXqCPKRg_4vA/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1AvEcO2Cdp0WldKFv2jgSfpmQTlvSvPRx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jGCyph761elgX5LxhvELx4P4WnDL6rIw/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1t5iZPoGpphPPSGJimdT--HhXYjBniCLP/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/18QucXLxZTH654KBYCHdYaOsnnypx9feI/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/13oTDzDW3JzV2wQILfKezfl3xmXdT8uyc/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1SVQXdxCPpj_XGtXtJQ55jvebjl6lhHST/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IEkAGJuoz1YFkyooQRLoGW-nqcLI7p-y/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JvLMkCCNR9CjUGT1KUnqPykLOivYi8Df/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jzx2d2aQQBDTQSsIjX3prjiFyls7y1sA/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/134zJZG_GvAyRdwaQNQJpTi3A7LTVAP3b/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xh_SJO6zmhdn8xG1akxfBjUVXO79pgTd/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-49. Creator An entity primarily responsible for making the resource Bereket Haileab #Granite adamellite albite Belview MN Biotite Biotite to chlorite alteration Chlorite (pennite) Feldspar alteration felsic felsic igneous rock granite igneous microcline Minnesota Minnesota River Valley monazite Montevideo Gneiss Morton Gneiss muscovite myrmekite Neoarchean orthoclase Oxides plutonic Quartz Sacred Heart Sacred Heart Granite sericite alteration sericitization Sphene Titanite Zircon https://bereket-haileab.geology.sites.carleton.edu/files/original/9df20a9ec7cacc81071658ebf6912d6c.jpg 9aa0dc56c00cad462f0bf3e9610b2f96 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-50 Subject The topic of the resource Duluth Gabbro Description An account of the resource Major Mineral: anorthite, orthopyroxene, clinopyroxene, olivine<br />Minor Minerals: oxides, biotite<br /> <p><strong>BH250-50 — Duluth Gabbro (Duluth Complex, Minnesota)</strong></p> <p data-start="60" data-end="990">BH250-50 represents one of North America’s most famous intrusive igneous rocks—the<span>&nbsp;</span><strong data-start="143" data-end="160">Duluth Gabbro</strong>, part of the immense<span>&nbsp;</span><span>Duluth Complex</span><span>&nbsp;</span>in northeastern Minnesota. This spectacular Mesoproterozoic intrusion formed approximately<span>&nbsp;</span><strong data-start="311" data-end="336">1.1 billion years ago</strong><span>&nbsp;</span>during the development of the<span>&nbsp;</span><span>Midcontinent Rift System</span>, a major tectonic event that nearly split the North American continent apart. As mantle-derived magmas rose into the crust during rifting, enormous volumes of mafic magma ponded and slowly crystallized to form one of the largest layered mafic intrusions in the world. The Duluth Complex covers thousands of square kilometers and remains one of the most studied examples of magmatic differentiation, crystal settling, and ore-forming processes in layered intrusions. Several samples in this collection—including BH250-11, 50, 113, 189, 192, and 193—come from this remarkable geologic system.</p> <p data-start="992" data-end="1873">In hand sample, BH250-50 displays the classic appearance of a coarse-grained mafic intrusive rock. The specimen is dominated by dark pyroxene-rich minerals intergrown with lighter plagioclase feldspar, producing the familiar black-and-white “salt and pepper” appearance common in many gabbros, although this sample leans distinctly darker because of its abundant mafic phases. The coarse grain size reflects slow cooling deep within a large magma chamber, where crystals had sufficient time to grow. The hand sample also hints at the layered nature of the Duluth intrusion, where changing proportions of plagioclase, pyroxene, olivine, and oxide minerals record shifts in magma chemistry through time. At many field localities in the Duluth Complex, spectacular rhythmic layering is visible in outcrop, preserving evidence of crystal accumulation on the floor of the magma chamber.</p> <p data-start="1875" data-end="2827">The thin sections beautifully illustrate the mineralogy of this sample. Large lath-shaped plagioclase crystals dominate many fields of view and display well-developed<span>&nbsp;</span><strong data-start="2042" data-end="2075">polysynthetic albite twinning</strong>, producing the characteristic striped appearance under crossed polarized light. These plagioclase crystals are compositionally calcium-rich, ranging from labradorite to bytownite and, in some zones, approaching anorthite-rich compositions. Intergrown with the feldspars are both<span>&nbsp;</span><strong data-start="2355" data-end="2372">clinopyroxene</strong><span>&nbsp;</span>and<span>&nbsp;</span><strong data-start="2377" data-end="2394">orthopyroxene</strong>, which appear as darker minerals in plane-polarized light and display higher-order interference colors under crossed polars. Some pyroxene grains show alteration along fractures and grain boundaries, while minor biotite occurs in localized areas. Oxide minerals appear as opaque black grains throughout the section, and some portions of the sample preserve evidence of late-stage alteration products associated with evolving fluids.<br /><br /></p> <p><span style="color: black;">One of the most striking features of BH250-50 is its well-developed<span class="apple-converted-space">&nbsp;</span><strong data-start="318" data-end="340">phaneritic texture</strong>, a hallmark of intrusive igneous rocks that cooled slowly at depth. The individual mineral grains are large enough to be easily recognized in hand sample, reflecting prolonged crystallization within a large magma chamber beneath the surface. The coarse-grained texture records slow conductive cooling and allowed plagioclase, pyroxene, olivine, and oxide minerals to grow into well-formed crystals. This texture alone tells students that the rock formed deep underground rather than at the surface, where rapid cooling would have produced a much finer-grained volcanic equivalent such as basalt.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="938" data-end="1681"><span style="color: black;">The thin section also reveals excellent examples of<span class="apple-converted-space">&nbsp;</span><strong data-start="990" data-end="1012">poikilitic texture</strong>, where large pyroxene crystals enclose numerous smaller plagioclase laths. In several photomicrographs, larger mafic minerals appear to wrap around or engulf earlier-formed feldspar crystals, producing a classic poikilitic relationship. When these enclosing crystals become especially large, they are referred to as<span class="apple-converted-space">&nbsp;</span><strong data-start="1329" data-end="1343">oikocrysts</strong>, and the smaller enclosed crystals are called<span class="apple-converted-space">&nbsp;</span><strong data-start="1390" data-end="1405">chadacrysts</strong>. These textures indicate that plagioclase crystallized earlier in the magma’s history, followed by later growth of pyroxene that surrounded previously formed crystals. This sequence provides valuable evidence for interpreting the crystallization history of the magma chamber.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="1683" data-end="2241"><span style="color: black;">Some portions of the thin section also display<span class="apple-converted-space">&nbsp;</span><strong data-start="1730" data-end="1764">subophitic to ophitic textures</strong>, where elongate plagioclase laths are partially enclosed by larger pyroxene crystals. While these textures are commonly associated with diabase, they may also occur in slowly cooled gabbroic systems where crystal growth relationships vary locally. In BH250-50, these textural variations suggest that crystallization conditions were not uniform throughout the magma chamber and may reflect local changes in cooling rates, magma replenishment, or crystal accumulation processes.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="2243" data-end="3026"><span style="color: black;">In addition to these intergrowth textures, some portions of the rock display classic<span class="apple-converted-space">&nbsp;</span><strong data-start="2328" data-end="2349">cumulate textures</strong>, which are especially important in layered intrusions such as the Duluth Complex. The framework of early-formed plagioclase and mafic minerals suggests periods of crystal settling and accumulation on the floor of the magma chamber. Depending on the proportion of trapped intercumulus melt, these textures may range from<span class="apple-converted-space">&nbsp;</span><strong data-start="2670" data-end="2693">adcumulate textures</strong>, where crystals fit tightly together with little remaining melt, to<span class="apple-converted-space">&nbsp;</span><strong data-start="2762" data-end="2787">mesocumulate textures</strong>, where intercumulus material remains between earlier-formed grains. These textures provide direct evidence that the Duluth magma chamber was an active and evolving system where crystals were constantly growing, settling, and reorganizing.<o:p></o:p></span></p> <p style="caret-color: #000000; font-variant-caps: normal; orphans: auto; text-align: start; widows: auto; -webkit-text-stroke-width: 0px; word-spacing: 0px;" data-start="3028" data-end="3468" data-is-last-node="" data-is-only-node=""><span style="color: black;">Together, these textural relationships make BH250-50 an exceptional teaching sample because students can move beyond simply identifying minerals and begin reconstructing the physical history of the magma chamber itself. The textures preserve a record of crystal growth, settling, enclosure, and magmatic evolution—showing that every crystal not only records chemistry, but also tells part of the story of how this enormous intrusion formed.<o:p></o:p></span></p> <p data-start="2829" data-end="3774">Anotehr important geological lessons preserved in BH250-50 is the process of<span>&nbsp;</span><strong data-start="2914" data-end="2965">fractional crystallization and crystal settling</strong><span>&nbsp;</span>within large magma chambers. Early-forming minerals such as olivine and calcium-rich plagioclase crystallized first and, because they were denser than the remaining melt, often settled to the chamber floor to form cumulate layers. As the magma evolved, pyroxenes and oxide minerals crystallized, producing the rhythmic layering so characteristic of the Duluth Complex. These textures remind students that magma chambers are dynamic environments rather than static pools of melt. Crystals grow, settle, react, and sometimes become resorbed as fresh magma enters the chamber. Much like I often tell students, magma systems rarely behave in the neat, predictable ways shown in simplified diagrams—they are constantly evolving systems responding to chemistry, temperature, density contrasts, and recharge events.</p> <p data-start="3776" data-end="4392">Geochemically, the Duluth Gabbro is mafic to locally ultramafic, enriched in<span>&nbsp;</span><strong data-start="3853" data-end="3895">iron, magnesium, calcium, and titanium</strong>, while relatively depleted in silica and alkalis. Basal portions of the intrusion contain elevated concentrations of chromium and nickel, reflecting early accumulation of olivine and pyroxene. Some evolved portions show moderate enrichment in light rare earth elements and may display negative europium anomalies linked to plagioclase fractionation. These geochemical patterns provide powerful evidence for long-term magmatic differentiation and repeated injections of new magma into the chamber.</p> <p data-start="4394" data-end="5083">The Duluth Complex is also economically important because it hosts significant deposits of<span>&nbsp;</span><strong data-start="4485" data-end="4563">nickel, copper, cobalt, platinum-group elements, titanium, and iron oxides</strong>, making it both a scientific treasure and a major resource target. Beyond its economic value, however, BH250-50 serves as an outstanding teaching specimen because it captures the complexity of large igneous systems—where tectonics, magma evolution, mineral chemistry, and time all intersect. It is a classic rock that tells an extraordinary story: nearly a billion years ago, a continent tried to tear itself apart, and this gabbro crystallized deep beneath that failed rift, preserving the evidence in every crystal.</p> <p>The geochemistry of the Duluth Gabbro provides another powerful line of evidence for understanding how this enormous magma chamber evolved through time. Compositionally, the rocks range from<span>&nbsp;</span><strong data-start="408" data-end="431">mafic to ultramafic</strong>, reflecting different stages of crystallization and crystal accumulation within the intrusion. They are typically enriched in<span>&nbsp;</span><strong data-start="558" data-end="620">iron (Fe), magnesium (Mg), calcium (Ca), and titanium (Ti)</strong>—elements commonly concentrated in early-forming mafic minerals such as olivine, pyroxene, and Fe-Ti oxides—while remaining relatively depleted in silica and alkali elements compared to more evolved igneous rocks. The basal ultramafic portions of the complex commonly contain elevated concentrations of<span>&nbsp;</span><strong data-start="923" data-end="940">chromium (Cr)</strong><span>&nbsp;</span>and<span>&nbsp;</span><strong data-start="945" data-end="960">nickel (Ni)</strong>, which strongly suggest early accumulation of olivine and pyroxene-rich cumulates. These chemical signatures are important because they preserve evidence of the earliest stages of magma differentiation, when dense minerals settled out of the melt and accumulated along the floor of the magma chamber.</p> <p data-start="1263" data-end="2293" data-is-last-node="" data-is-only-node="">Rare Earth Element (REE) patterns add another layer of insight into the magmatic evolution of the Duluth Complex. Many samples show moderate enrichment in<span>&nbsp;</span><strong data-start="1418" data-end="1455">Light Rare Earth Elements (LREEs)</strong><span>&nbsp;</span>relative to Heavy Rare Earth Elements (HREEs), indicating that the parental magma was not entirely primitive and may have experienced crustal interaction or repeated magma recharge events. Some of the more evolved portions of the intrusion also display<span>&nbsp;</span><strong data-start="1709" data-end="1745">negative europium (Eu) anomalies</strong>, which are commonly interpreted as evidence for significant plagioclase fractionation because europium can substitute into calcium-rich feldspar during crystallization. In simpler terms, the chemistry confirms what the textures already reveal under the microscope: this was a dynamic magmatic system where crystals were continuously forming, settling, and chemically modifying the remaining melt. The Duluth Complex is therefore an excellent example of how mineralogy, textures, and geochemistry work together to tell a much larger magmatic story.</p> <br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=465689726&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Duluth Vistor Center, Minnesota, USA GPS Location: 46°43'46.78"N, 92°12'25.09"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 50. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=0b150934e7814b55bdc58801ec96007d" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=0b150934e7814b55bdc58801ec96007d">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fUNQygsDUGWh2uioIv4_3m95j14Tcl6c/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_DU0qXtZH5gFgkCY2lNJWAMlhPR4VyQv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/13i2gnlEiirls-JtHtkTRrmASOGBjaWud/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/12AS610Z6Q2am611Lz81VwswSGwyojqKt/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Wj69_FJPwb1y4yKduY87HaH9bXXNxHxu/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1csJKAy54XbxeNjNy9O5_n6xAk9Ep0gke/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_MmFuoNFreZtnPmBHExdhnpoCT-THecX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hYeDn7bn6g8CP9SAzF48R-3NlMoXwgrS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1yIe4ihnVIjnjpk9aW2qHvn8mcJWnD6YL/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1eBvT6zd3Nv1-7XrQ69cA7HpnPbQ8B-JY/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1AjvWlfX-En-x2z8MqMHOEziaurzX0HQO/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10kwsVApt1H2DPwi9Tp3bZZ2Z1B32DHwg/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1z36GgKb0FCa-MeGGAgcisTzytcESapND/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/16KMy2UaNriwbt8uSO3vS4cnrDp5cLcdL/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-50. Creator An entity primarily responsible for making the resource Bereket Haileab adcumulate anhedral pyroxenes Anorthite Biotite chadacryst Clinopyroxene Crystal Settling cumulate layering cumulate rock Cumulate texture Duluth Duluth Complex Duluth Gabbro euhedral olivine euhedral plagioclase Fractional crystallization gabbro igneous Ilmenite interstitial interstitial pyroxenes and oxides layered cumulate texture Layered intrusion Layered mafic intrusion mafic mafic differentiation Mafic Intrusive Rock Magmatic Differentiation Magnetite mesocumulate Mesoproterozoic geology Midcontinent Rift Minnesota geology nickel copper deposits oikocryst olivine olivine rimmed by orthopyroxene ophitic texture Orthopyroxene Oxide minerals Oxides Phaneritic texture Plagioclase platinum group elements plutonic poikilitic texture rhythmic layering Subophitic texture ternary phase diagram example https://bereket-haileab.geology.sites.carleton.edu/files/original/89771b9f441598e93619da40e789db2d.jpg 6d0780c76280db3d95eeca2b869d29ad Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-53 Subject The topic of the resource Metagabbro Description An account of the resource Major Minerals: quartz, plagioclase, hornblende, clinopyroxene (augtie), hypersthene, bronzite<br /><br />Optics: some of the pyroxens show excellent cleavages<br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1637068568&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Granite Falls, Minnesota, USA GPS Coordinates: 44 48 10.20 N, 95 32 52.55W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-53. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=a0ea8d03cd3c4bce957402f96e7d6800" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=a0ea8d03cd3c4bce957402f96e7d6800">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/13X3vdnCRuQEc6IgFp2SyBzdrjfSbTqgq/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1INPetHKTrFyftrEPc7DPUdjeT8pPxSjv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1vBytZZ-owGnjnZNQ_ZsgA7LACX10cn6c/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1yBwG2ieVu3PyaRVFAwNySquw1lz66Aku/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kVFZBVE2i4qSJmC-SYMjdE92zdyjTFN5/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1cxMlKpppyoSqe26pBALAaPALVdrlwu4w/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1D-AAtudLDEz-7h_1_zkr_82ME8PyX8Op/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1yb0taQkYGc_LZzLZ7E5UVc6ivUtfHPSR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XUzrmp5U0VdzN0ob0C5v0Ue2R0sKfNzp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1DVR7e6xS_oSxwAl-9F7HuXr8zSc2Q1kT/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1WJC0mYnfrzCXj3xPhb3qNb2MjMC38Lwr/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-53. Creator An entity primarily responsible for making the resource Bereket Haileab Amphibolite to Granulite Facies Augite basalt Bronzite Granite Falls Geology Hornblende Hypersthene Metagabbro metamorphic Metamorphosed Mafic Rock metavolcanic Midcontinent Geological Province Minnesota geology Minnesota Rive Valley Geology Plagioclase Pyroxene Cleavage https://bereket-haileab.geology.sites.carleton.edu/files/original/b70469fc2c706ad21b08bd0d92e79f18.jpg 0286ac920eab86e312269187fa18f1b5 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-60 Subject The topic of the resource Basalt; Basanite Description An account of the resource Major Minerals: hauyne, pyroxene, titanaugite, plagiocalse<br />Minor Minerals: olivine, aegirine, oxide, biotite, apatite <br />Mineralogy Comments: hauyne, biotite is groundmass<br /><br />Texture: porphyritic, vesicular, zoned titanaugite<br /><br /><span><span><span>Optical Features: Titanaugite displays anomalous interference colors. Aegirine-augite zoned by titanaugite crystals. </span></span></span>Altered pyroxenes to iddingsite (clay minerals, iron oxides) due hydration and oxidation processes.<br /><br />In these thin sections, the early-formed aegirine-augite becomes unstable and is rimmed by or replaced with augite. This transformation may result from fractional crystallization, where silica increases in the melt, and/or from changes in oxygen fugacity. Under the microscope, this is evident as zoning, with greenish aegirine-augite cores surrounded by brownish augite rims. You may also observe reaction textures, such as partial replacement or corona structures, a decrease in pleochroism toward the rim (as augite is less pleochroic), and changes in extinction angles and interference colors across the grain. <p><br />Glomerocryst, an aggregate or clump of two or more crystals (usually phenocrysts) that appear to have grown together or accumulated before or during crystallization.</p> <p data-start="46" data-end="313">BH250-60 was specifically collected and prepared for the study of the mineral hauyne. <span>The sample was collected by Sarah Greene Hoffmann ’05 during a University of Wisconsin petrology field trip to the Canary Islands.</span> There are 15 thin sections available, each containing beautiful crystals of hauyne.</p> <p data-start="315" data-end="625">Hauyne is a sodium-rich, sulfate-bearing feldspathoid belonging to the sodalite group. It plays an important role in the petrology of silica-undersaturated igneous rocks. Common rock types in which hauyne occurs include phonolite, nephelinite, tephrite, and hauyne-bearing basanite.</p> <br /><br /><span>Note on Anomalous Interference Colors:</span><br /><span>Titanaugite contains significant titanium (titaniume oxides of 3.7 wt. % in this rock), which enhances pleochroic absorption. This strong absorption alters the behavior of light as it travels through the crystal, causing deviations from the typical interference colors expected from its birefringence. These anomalous interference colors are primarily due to intense absorption linked to titanium and iron content, a phenomenon known as anomalous interference coloration.<br /></span><br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=161782510&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Canary Islands Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-60. Housed at Carleton College in Minnesota. Contributor An entity responsible for making contributions to the resource Bereke Haileab Sarah Greene Hoffmann, '05 Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=4f56812635fa4cd2ac0dea827c20a924" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=4f56812635fa4cd2ac0dea827c20a924">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/18HIGLjZ0L4x1-vHR6t2ZcU-JcQoK9RGj/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1K68SjB4150lQAp5zfBWVNKrbt519Lw9c/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1n63Jd19NgF2z_xdTetLIV00AnST61EQV/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1TA3ag_6aXYdxGAKWNXwrDTLwcQXrsQLj/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1K4cW9HnzdVLg5iqkXJz7ZRr3t9Vc5m8n/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1YUw-x65JxlqV0LphtrLwQ8v8GABUX6IP/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/13sQhfROyGpDxfCbUQGY83Y1A3J-wEfBS/preview" allow="autoplay"></iframe><br />Augite interference figure<br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IXuwPDHUUQUDHMOPIvLUG2xNJgd_cyET/preview" allow="autoplay"></iframe><br />TAS diagram of sample 60. Creator An entity primarily responsible for making the resource Bereket Haileab Aegirine-augite Alkali basalt Anomalous interference colors basalt basanite Canary Islands Corona textures Crystal zoning Feldspathoid minerals Fractional crystallization Glomerocryst hauyne Hauyne-bearing basanite Iddingsite (alteration product) igneous Isotropic minerals Istotropic hauyne mafic olivine Optical zoning Oxides Plagioclase porphyritic texture Pyroxene Pyroxene hydration Pyroxene replacement Reaction rims Sarah Greene Hoffmann '05 Silica-undersaturated igneous rock Silica-undersaturation Sodalite group minerals Titanaugite Titanaugite interference colors Titanaugite optical properties vesicular texture volcanic Zoned pyroxene Zoned titanaugite https://bereket-haileab.geology.sites.carleton.edu/files/original/57d598907ecdfe1840966efb80545c9c.JPEG a50e1e02b4e6deda88b2da44fa71799e Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-60b Subject The topic of the resource Hauyne Phonolite Description An account of the resource Major Minerals: Hauyne, titanaugite, plagioclase, oxides Optical Properties: Hauyne: Beautiful, fuzzy, bluish isotropic crystals. Titanaugite: Exhibits pronounced anomalous interference colors. Mineralogical Notes: Hauyne is a sodium-rich, sulfate-bearing feldspathoid mineral in the sodalite group. It is a key indicator of silica-undersaturated magmatic systems and typically occurs in phonolite, nephelinite, tephrite, and hauyne-bearing basanite. Note on Anomalous Interference Colors: Titanaugite in this sample contains elevated titanium (3.7 wt.% TiO₂), contributing to strong pleochroic absorption. This absorption affects the transmission of light through the crystal, leading to deviations from standard interference colors based on birefringence alone. The resulting effect known as anomalous interference coloration is primarily caused by high titanium and iron content. Provenance and Special Note: This sample was collected from Tahiti by the late Dr. Francie H. Brown (University of Utah). Two thin sections were prepared: one remains in the BH250 collection, and the other is housed at the University of Utah. According to Dr. Brown, the original outcrop is no longer accessible due to the construction of an airport tarmac. Students in mineralogy courses at Carleton have consistently admired this thin section especially for its striking hauyne. Please handle this irreplaceable sample with great care. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Tahiti Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-60b. Housed at Carleton College in Minnesota. Contributor An entity responsible for making contributions to the resource Frank Brown Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=a942659101d6430bb6a273770b2bacca" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=a942659101d6430bb6a273770b2bacca">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dnaN_YYnTw0y4R8f5Uglt28lfggq5eO6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jL1uTaka-CiYSI-QLwC_1G7mSq-1C-cH/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fYyCo2QRgRKBuJHVFK4QnpgQzeFKLuzp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1UkRbrhAiyouqIWqMVkWsjQzwjHiwZsUS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/16hOQ4F0Vs-sUOIHWo3j-trm4OJByzHSR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BKQVZCWHfL6FvI-fymWddprGlpx0TjAX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1B8mfYTRf71xp1woperEa-kWl6o38Ca7U/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19JZ1v4L6YXbzJL4XOPFrvvY-zVIFJA9e/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Anomalous interference colors Feldspathoid hauyne igneous intermediate Isotropic crystals phonolite Plagioclase silica-undersaturated Sodalite group Sodium-rich mineral Tahiti Titanaugite Titanium-rich pyroxene volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/5307ceecb7c04631f4c48dd589219ed0.jpg de6396e750bb8c4a6a13f819011c014f Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-63 Subject The topic of the resource Granodiorite Description An account of the resource Major Minerals: orthoclase, quartz, biotite Minor Minerals: chlorite, zircon, titanite, hornblende, albite, epidote BH250-63 is a granitic sample collected from Confusion Point, a geologically significant outcrop in northern Minnesota, situated within the Giants Range Batholith. At Confusion Point, the exposure provides striking evidence of multiple phases of magmatic intrusion. Road cuts reveal a network of cross-cutting relationships between lighter-colored granitic bodies and darker amphibolite dikes or enclaves, highlighting a long history of successive intrusion, deformation, and recrystallization. These features make Confusion Point a classic location for studying Archean crustal evolution and the structural complexity of ancient continental lithosphere. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Confusion Hill, Minnesota, USA GPS Coordinates: 47°34'41.31"N, 92°32'41.00"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 63. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=360f3683ab77404b8ea5ce91cc63cebf" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=360f3683ab77404b8ea5ce91cc63cebf">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Py1IFSy8uX4zO6R-uKmqxnoxwMFiBABF/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1CG1WwDoM8CkINXSgBJ9W1TFRNywymtlm/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1TK60dmMNAUEmMPclfyBNxLrCq19xSmuw/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1GaUdp61O4oObpjCTiUvAdOWEIrSTodY8/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1KOikqSyVf_Ec25QtW9YHKKcs47lSpuW-/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Q8ijkyg7y0UgXpMbRtrE6bhEPtbdNIRl/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hnnSZuPAcp8Vg8cxJObNNlWTFB8m3O0Q/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Archean Granite Confusion Point Cross-cutting Relationships Crustal Evolution felsic Giants Range Batholith granodiorite igneous Multiple Intrusion Northern Minnesota Geology plutonic https://bereket-haileab.geology.sites.carleton.edu/files/original/8e3d5b8c495decc861521fd4223dde57.jpg b6118f5f348ee197d845a698ec08686a Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-71 Subject The topic of the resource Granite Description An account of the resource Major Mineral: quartz <br />Minor Minerals: chlorite, oxides<br /><br /> <p>BH250-71 is a granitic rock collected near Split Rock Lighthouse along the North Shore of Lake Superior. It is highly altered, with all the plagioclase and orthoclase feldspars replaced by sericite and clay minerals. Despite this alteration, the quartz crystals remain pristine. This unit is likely the intrusive equivalent of BH250-72, the rhyolites associated with the North Shore Volcanics. The well-preserved quartz crystals in BH250-71 are suitable for obtaining uniaxial interference figures and flash figures under a polarizing microscope.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1341462357&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Nearby Geographic Feature: Splitrock Lighthouse GPS Coordinate: 47°12'0.09"N Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 71. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=432562de55ff4ba8aa78c7d6bb8d0be1" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=432562de55ff4ba8aa78c7d6bb8d0be1">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1aubf4LBh4xe_R4RCSUphT10jbqbJwz66/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1aFBxvL4ZVnRABpsy2yIgZiW6Qq4snLam/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RmsJC9GmR82jjU5OfNIuqejARaa0irV6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1NKMd0dxO7yVJLnvRuM2g1fO8yGLwh8Vh/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kbqyBoX91eWQG_zsbvxWrWKq6k7T5MgN/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14VuNhrwGRDEJWlQdWArO7HridCvdydud/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1a_tb5xCBeNU3CJs2MW3sVdLwHeeLwzK5/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QuycX8XZpSTAzrBQfpXL2Xl_Hbf3F1Qa/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-71. Creator An entity primarily responsible for making the resource Bereket Haileab Clay alteration felsic Flash figures granite igneous Interference figures Intrusive felsic rock North Shore Volcanics plutonic Quartz interference figures sericitization Split Rock Lighthouse https://bereket-haileab.geology.sites.carleton.edu/files/original/03e2bbbed69630075576b46140fc10ca.jpg 08cbca5eac0f39df352b6bc28c7105a9 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-72 Subject The topic of the resource Rhyolite Description An account of the resource Major Mineral: quartz <br />Minor Minerals: glassy groundmass, plagioclase, altered biotite<br /><br /><br />BH250-72 is a rhyolite sample collected from Shovel Point, located along the North Shore of Lake Superior in Minnesota. This outcrop is part of the Midcontinent Rift System and represents one of the oldest felsic volcanic rocks in the region, dating back to approximately 1.1 billion years ago. Chemically, BH250-72 is a felsic rock with high silica content (SiO₂ &gt;70%), setting it apart from the dominant basalt flows of the North Shore. It is enriched in alkali elements(Na₂O + K₂O), classifying it as a rhyolite, though in some flows, it verges on high-silica dacite. Trace element data show enrichment in incompatible elements such as Rb, Th, U, and light rare earth elements (LREEs). Mineralogically, BH250-72 is composed primarily of quartz, K-feldspar (orthoclase or microcline), sodic plagioclase, and devitrified volcanic glass. Minor and accessory minerals include biotite, magnetite/ilmenite, zircon, and apatite. The rock exhibits classic rhyolitic textures such as flow banding and spherulites, and contains phenocrysts of quartz and feldspar within a fine-grained or formerly glassy groundmass. The presence of rhyolite in this predominantly mafic volcanic sequence reflects significant magmatic differentiation of the parent mafic magmas, likely related to the processes that also formed the Duluth Gabbro Complex.<br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1549324518&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Shovel Point, Minnesota, USA GPS Coordinates: 47°20'22.53"N, 91°11'6.11"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 72. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=7e843f1e394f4527b38b0bd1ef830667" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=7e843f1e394f4527b38b0bd1ef830667">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jeLyhEPBJsjPUB_itx0QP6m7PX-bl4ju/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/13T9T9rk-4oAAsFifoa0ERf97NQYWfp8b/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pJhUh7N1MM1gMz_02gVad4wmCXI0IqYR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/191Vkr70M5ey0l_pDr3DDNH9N-t3nTxNC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10j8wQAj_vJutYLdzkj_gu-As9x2auPrM/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1n3uDZR4Vx7NVl0i4TGDQeJKAzLnHauNK/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1EXJyJLvyDOFA6m7nQzpGxuteXX8qVryw/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gVkJrpcoyhoP1oABz8nFeGju1mh_7Izk/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1WW-vkdS-TDSySv-jz3FR_vbfbz7iW-I-/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15-3de4hx7UsRPUP6EBZq8YeepsGjFMcn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1M9u6UH-mp8DUm4TxlrXMKhkHBb99xHft/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-72. Creator An entity primarily responsible for making the resource Bereket Haileab Devitrified Glass Duluth Gabbro Complex felsic Felsic Volcanic Rock High-silica rhyolite igneous Lake Superior geology Magmatic Differentiation Midcontinent Rift Minnesota geology North Shore Volcanic Group Phenocrysts Quartz rhyolite Shovel Point volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/551cb9402c37a007bb5da344c3722a19.jpg 6b388a363c711d750905551ac1af59a9 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-75 Subject The topic of the resource Granite Description An account of the resource Major Minerals: orthoclase, plagioclase Minor Minerals: biotite, quartz, chlorite Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Confusion Point, Minnesota, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 75. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=faa1257da57a4c4294d14e04ef5556e5" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=faa1257da57a4c4294d14e04ef5556e5">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1L95FDmHhUhR5b0IbKgPMIuzxLE_Sji3t/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Hu3KFdRvlxIVA956_hHU2NpsP4pxVOio/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/11S67zRE0pLxkGkACBrFbJUyrshweYo_u/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bhe56yxfryOUMpn7xeW-tWhWtq6SXO3r/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab felsic granite igneous plutonic https://bereket-haileab.geology.sites.carleton.edu/files/original/c86a37d017358581bca00cdc80634184.jpg 7a58e6d4ed88c633560008050b0fc6bd https://bereket-haileab.geology.sites.carleton.edu/files/original/c6a120d2bc7ff9c167a4b808baf55cb4.jpg b8f54a9ed14ced58b62422a4a74a02a3 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-81 Subject The topic of the resource Granite Zircon-rich, REE-bearing perthitic granite Description An account of the resource Major Minerals: perthite, antiperthite, albite, hornblende, quartz, fluorite Minor Minerals: microcline, zircon, biotite, sphene (titanite), spinel, monazite, allanite Mineralogy Comments: large zoned zircons; hornblende altered to chlorite; allanite mostly altered; euhedral monazite common BH250-81 is one of the finest accessory-mineral-rich granitoids in the BH250 Collection and serves as an exceptional teaching specimen for mineralogy, igneous petrology, geochronology, and crustal evolution. Although the rock is dominated by feldspar, quartz, hornblende, and biotite, its greatest scientific value lies in the remarkable abundance of zircon, monazite, titanite, allanite, fluorite, and other trace minerals preserved throughout the thin section. The rock exhibits a coarse-grained phaneritic texture characteristic of slow crystallization at depth. Large feldspar crystals dominate the rock and display spectacular perthitic and antiperthitic exsolution textures. Quartz occurs as anhedral interstitial grains occupying spaces between feldspars, while hornblende and biotite form scattered mafic aggregates. Some hornblende crystals show alteration to chlorite, indicating late-stage fluid interaction after primary crystallization. The feldspars are among the most instructive features of the sample. Numerous crystals display both coarse patch perthite and fine string perthite produced during slow cooling. These exsolution textures formed when high-temperature alkali feldspars became unstable during cooling and unmixed into potassium-rich and sodium-rich phases. Some crystals display antiperthitic textures in which potassium feldspar occurs as exsolved blebs within plagioclase hosts. Together these textures provide a textbook example of feldspar re-equilibration below the solvus and record the prolonged cooling history of the intrusion. The most remarkable feature of BH250-81 is its extraordinary population of zircon crystals. Many zircons are unusually large, euhedral, and exceptionally abundant. Several preserve internal growth zoning, while others display extensive networks of fractures and mosaic textures produced by metamictization. Metamictization occurs when the decay of uranium and thorium damages the zircon crystal lattice over geologic time. The resulting crackled appearance provides direct petrographic evidence of radioactive decay and makes these zircons ideal teaching examples for geochronology courses. Many zircon grains occur in clusters associated with biotite-rich domains and late-stage interstitial phases. Some crystals preserve concentric growth zones that record changing magma chemistry during crystallization. Others display varying degrees of radiation damage, illustrating how crystal structures evolve through time as radioactive isotopes decay. Few teaching collections contain zircon populations that so clearly demonstrate both magmatic growth and post-crystallization radiation damage. Monazite and allanite are also present and contribute to the rare-earth-element budget of the rock. Monazite occurs as euhedral grains and represents an important host for thorium and light rare-earth elements. Allanite is commonly altered but remains recognizable as a rare-earth-rich accessory mineral associated with late-stage magmatic differentiation. Titanite (sphene) is also present and provides an additional repository for uranium, thorium, and rare-earth elements. The abundance of zircon, monazite, allanite, titanite, and apatite makes BH250-81 an outstanding natural laboratory for discussing modern geochronologic techniques. These minerals are routinely used for U-Pb, U-Th-Pb, and isotopic studies that constrain crystallization ages, metamorphic events, cooling histories, and crustal evolution. Students examining this thin section can directly observe the minerals that geochronologists separate, analyze, and interpret to reconstruct Earth history. BH250-81 beautifully illustrates the connection between classical petrography and modern geochemistry. The sample demonstrates how textures observed under the microscope—from feldspar exsolution and amphibole alteration to zircon zoning and metamictization—can reveal processes operating over hundreds of millions to billions of years. It is therefore one of the most valuable geochronology and accessory-mineral teaching specimens in the BH250 Collection. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-81. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=7884c20d16a44364b1b43f463b0a38c6" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=7884c20d16a44364b1b43f463b0a38c6">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1imolG1tMIRbnyE17dS7c2XsWFwQDS2ZG/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wRqtPbm0rrwQ3ZCJmGbgn7Djk4Gfmi7B/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1meHCQRLaGLC8CkPIQkQFVDxOnKsu0Cae/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" 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src="https://drive.google.com/file/d/1Bd75ZRu_xFYaA9t-Hf_r3eSF4PUtjAYr/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1G-9VPDfuLztwmX2sclsdJXcpRBBST-qF/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1DeqBPdxdJgHbJGki5xHIJIhnUo9LY0im/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1Q_GjnuVRMcv_lqSq-onQIdjwqt-VNCKf/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1blsRH1IjoJp3xVyILWFSYUzS2rd6Qybn/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1_DxKtSM3EsKwQJZjQ3e_BlGrsbxGtAwX/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZLXX7tzD5_CBzWRweJ2DG3IrBQJCpxpX/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1dp4JEc-9Yl7CDTV0XyWakDeBvt6ixmUN/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/13qSGikCY4zA13FSZ7UuZVMkPWzjEXGz3/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/18jumiWOEkra08MLOmPcueoiOXqYYl9U3/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZcqpNNPwqBLEXfJe6vBCNjB_7qnlssaJ/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1p7ZWEDIPRPp0RRmcEmE8KUjB6FTlgDTd/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1rzDy09qw57YboLBkR4UutC6Dfi0OAz0l/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FbIWI9Gw3lbr1eY8Gp_kaL-J5BxqE4f3/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1F56xxtArzoXLPbqnbI2cK8a_KcL8UcAL/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab allanite Amphibole Alteration Antiperthite Apatite Biotite chloritization Coarse-grained Euhedral Zircon Exsolution texture Feldspar exsolution felsic Flame Perthite fluorite Hornblende igneous Metamict Metamict Texture Metamict Zircon monazite Oscillatory Zoning Patch Perthite Perthite Phaneritic texture plutonic Radiation damage Radiation Damage in Zircon rare earth elements REE Minerals Solvus Sphene Spinel String Perthite Subsolidus Titanite Zircon Zircon Separation zircon zoning Zoned Zircon Zoning https://bereket-haileab.geology.sites.carleton.edu/files/original/e3f28262ff1d747250946df8eeb0e0e9.jpg 51058bcab9e0ca4456bb432398ca01a6 https://bereket-haileab.geology.sites.carleton.edu/files/original/dc2dcb5b29ac5f9abe01d281fa3671aa.jpg e11c5ca0922ea433a2e9ff6e95e0b307 https://bereket-haileab.geology.sites.carleton.edu/files/original/1ea8bf1fe3a3b7504ee8e50873aa2f25.jpg df21ea0149c408b15ff7f8c9201130e6 https://bereket-haileab.geology.sites.carleton.edu/files/original/33bf877ac23943b2933c9f16650979b5.jpg 558b9754d4b1b01fd07432772635376b Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-82 Subject The topic of the resource Olivine Basalt Description An account of the resource <p><strong>Major Minerals:</strong>&nbsp;olivine (forsterite-rich), augite, plagioclase feldspar, volcanic glass</p> <p><strong>Minor Minerals:</strong>&nbsp;magnetite and other Fe–Ti oxides</p> <p>BH250-82 is one of the finest olivine basalts in the BH250 Teaching Collection and among the most popular samples used in introduction to geology, mineralogy and petrology laboratories. Collected during a visit to the Big Island of Hawaii, the specimen contains abundant green olivine phenocrysts enclosed within a dark vesicular basaltic matrix. Several hand specimens and thin sections are available, including large samples that beautifully display the characteristic green olivine crystals for which Hawaiian basalts are famous.</p> <p>This specimen provides an outstanding introduction to basaltic volcanism, mantle-derived magmas, volcanic textures, mineral optics, and igneous petrology. Students can examine the same minerals in hand sample and thin section and relate crystal growth, cooling history, and optical properties to the evolution of basaltic magma.</p> <p><strong>Geological Significance</strong></p> <p>BH250-82 originated from a primitive basaltic magma generated within the Hawaiian mantle plume. Olivine was among the first minerals to crystallize from the hot magma at depth. These early-formed crystals remained suspended within the melt as it ascended toward the surface and were eventually erupted as lava.</p> <p>The abundant vesicles throughout the rock record the escape of dissolved volcanic gases during eruption and cooling. The combination of olivine phenocrysts and vesicular texture is characteristic of many Hawaiian basalts and provides evidence for both deep crystallization and shallow volcanic emplacement.</p> <p>The high abundance of olivine indicates crystallization from a magnesium-rich magma and reflects the mantle origin of Hawaiian hotspot volcanism.</p> <p><strong>Hand Sample Description</strong></p> <p>The rock is dark gray to black and displays a strongly porphyritic texture. Numerous green olivine phenocrysts, typically 1–4 mm in diameter, are scattered throughout a dark aphanitic groundmass. The olivine crystals are generally euhedral to subhedral and are readily visible without magnification.</p> <p>Abundant vesicles occur throughout the specimen and vary in size from less than a millimeter to several millimeters in diameter. These vesicles formed as volcanic gases escaped from the lava during eruption and cooling. The striking contrast between the green olivine crystals and the dark volcanic matrix makes this one of the most visually appealing volcanic rocks in the collection.</p> <p><strong>Petrography and Texture</strong></p> <p>Thin sections reveal a classic porphyritic volcanic texture consisting of large olivine and pyroxene phenocrysts surrounded by a very fine-grained groundmass composed of plagioclase microlites, pyroxene, volcanic glass, and opaque oxide minerals.</p> <p>The texture records a two-stage cooling history. The large olivine and pyroxene crystals formed during relatively slow cooling within a magma reservoir beneath the volcano. Following eruption, the remaining melt cooled rapidly, producing the fine-grained to partly glassy groundmass.</p> <p>The groundmass is dominated by abundant plagioclase microlites and tiny pyroxene crystals that exhibit a pilotaxitic texture typical of rapidly cooled basaltic lava. Vesicles are present in both hand sample and thin section, preserving evidence of volatile-rich magma during eruption.</p> <p>Several olivine crystals contain fractures and small inclusions that developed during crystal growth and cooling. The crystal boundaries are generally sharp and well preserved, indicating that the olivine remained stable throughout the final stages of crystallization.</p> <p><strong>Optical Mineralogy</strong></p> <p>BH250-82 is an exceptional teaching specimen for optical mineralogy.</p> <p>Olivine exhibits high relief, no cleavage, irregular fractures, and bright second-order interference colors under crossed polars. Several grains are cut nearly perpendicular to an optic axis and produce excellent biaxial interference figures. These grains display a large 2V angle approaching 90°, making them ideal for demonstrating optical orientation and interference figure analysis.</p> <p>Some olivine crystals show subtle undulatory extinction and internal strain features visible during stage rotation. These features likely reflect crystal-growth stresses, magma transport, or cooling-related deformation rather than regional metamorphism.</p> <p>Clinopyroxene (augite) displays moderate to high relief, characteristic cleavage, inclined extinction, and bright interference colors. The contrast between olivine and pyroxene provides an excellent opportunity for students to learn mineral identification and optical techniques.</p> <p><strong>Educational Value</strong></p> <p>BH250-82 is one of the most versatile volcanic rocks in the BH250 Collection and is particularly useful for teaching:</p> <ul> <li>Basalt petrology</li> <li>Hawaiian hotspot volcanism</li> <li>Mantle-derived magmas</li> <li>Olivine crystallization</li> <li>Porphyritic texture</li> <li>Two-stage cooling histories</li> <li>Vesicular volcanic rocks</li> <li>Volcanic gas exsolution</li> <li>Optical mineralogy</li> <li>Biaxial interference figures</li> <li>Determination of 2V angles</li> <li>Igneous textures</li> <li>Volcanic glass and microlitic groundmasses</li> <li>Ocean-island basalt (OIB) petrogenesis</li> </ul> <p>The combination of spectacular hand specimens, excellent thin sections, abundant olivine phenocrysts, and high-quality optical features makes BH250-82 one of the premier volcanic teaching samples in the collection.</p> <p>&nbsp;</p> <br /> <p data-start="573" data-end="672"><span>&nbsp;</span></p> <br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1323504118&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Discovery Harbor, Hawaii, USA GPS Coordinates: 18°56'4.42"N, 155°38'45.89"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-82. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=665cd35700f946d4a9bcc7b48396fbc5" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=665cd35700f946d4a9bcc7b48396fbc5">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1KXx5i3tihNw_G6x2vjUM1pQgRo4iNV7g/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1mV2zLFq0g3yVotdwPncGaqGMJtguWOAu/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1k-_4qllKTZ3jdk3SDmEsemVaKED0VDRT/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1epDk_0vP4AV5peHC7Zsnf8uJdbmN2ad0/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1qdNYbFGnmt6RYw6nAPpYB0rnbGkvw-Gs/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1oGihzyp23qDJNa8uA3DTLM8Hb33Y2TOp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1al8mB4d_nXRtaK7TbGU7OMIg5_vnXAGK/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1elgApsG1y8sWBqOsRO4hxq9jEHtRpNK3/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Dgaf4BO3Lv4iSKghzziU6Vxsa37An15v/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/12rwY2zf2l1XJysR9WS2993uI5-0O0k4m/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-82. Creator An entity primarily responsible for making the resource Bereket Haileab 2nd order interference colors 2V ~90° 2V angle Augite basalt basaltic composition biaxial Biaxial Mineral birefringence Discovery Harbor euhedral phenocrysts fine grained groundmass forsterite Green Sand Beach Hawaii Hawaiian basalt Hawaiian hotspot volcanism Hawaiian volcanism Hotspot Volcanism igneous interference figure magma evolution Mantle Plume Ocean Island Basalt OIB olivine Olivine Basalt Papakōlea phenocryst pilotaxitic texture porphyritic texture strong birefringence ultramafic undulatory extinction vesicular basalt vesicular texture volcanic Volcanic glass volcanic texture https://bereket-haileab.geology.sites.carleton.edu/files/original/240fd866934b27542358e92c414526b1.jpg f2d1a3f32edc7cc16d135acaf97a9c80 https://bereket-haileab.geology.sites.carleton.edu/files/original/58ce61aff6529539f57e68d0a99243e4.jpg be23e3f0a8ef7bf8b06776d4d5c2175d Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-83 Subject The topic of the resource Leucite Phonolite Leucitophyre Description An account of the resource Major Minerals: leucite, pseudoisotropic leucite, plagioclase Minor Mineral: clinopyroxene, orthopyroxenes, biotite, oxides, orthoclase Optics: pseudo isotropic, grid-like or tartan plaid-like patterns BH250-83 is an exceptional leucite-bearing phonolitic volcanic rock collected from the Bolsena–Civita Castellana region of central Italy, part of the Roman Magmatic Province. The sample is especially important because it preserves spectacular leucite phenocrysts displaying classic pseudoisotropic optical behavior, tartan-style internal twinning, and crystallographic textures produced during subsolidus phase transitions. The rock provides an outstanding teaching example for igneous petrology, optical mineralogy, crystallography, alkaline magma evolution, and feldspathoid stability. The hand sample shows abundant large leucite phenocrysts set within a fine-grained dark gray to black volcanic groundmass. Many leucite crystals are rounded to subhedral and display pale gray to whitish coloration in hand specimen. Several crystals are over one centimeter across and stand out prominently against the finer matrix. The overall appearance is strongly porphyritic, indicating a two-stage cooling history in which early leucite crystals formed slowly at depth before eruption or shallow emplacement of the remaining melt. Thin sections reveal remarkable optical textures within the leucite crystals, including pseudoisotropic behavior, weak birefringence, complex grid-like twinning, internal fractures, and faint domain structures related to cooling-induced symmetry changes. Unlike BH250-83b, this sample lacks prominent reaction rims around the leucite crystals, suggesting that the crystals remained in chemical equilibrium with the surrounding magma during crystallization and cooling. BH250-83 belongs to a family of potassium-rich alkaline volcanic rocks generated from silica-undersaturated magmas. The presence of abundant leucite instead of quartz is highly significant because leucite is stable only in magmas deficient in silica. In silica-rich systems, leucite reacts to form alkali feldspar and therefore cannot persist. The rock therefore records crystallization from an alkaline magma enriched in potassium and incompatible elements, characteristic of the Roman volcanic province of Italy. Leucite is the defining mineral of the rock and occurs as large phenocrysts throughout the sample. Under the microscope, the leucite commonly appears cloudy to weakly birefringent and contains distinctive internal twinning domains. Some crystals show inclusions of tiny opaque minerals and minute melt inclusions concentrated along fractures and internal zones. The groundmass consists primarily of tiny feldspathic laths and fine mafic minerals. The plagioclase microlites define a pilotaxitic to trachytic groundmass texture in places, suggesting flow alignment during final stages of magma movement and cooling. Pyroxenes occur as small subhedral crystals within the matrix and likely represent early mafic phases crystallized from the alkaline melt. Minor biotite indicates potassium enrichment and volatile-rich late-stage magmatic conditions. Hand Sample Description The hand specimen displays a striking porphyritic texture with abundant large leucite phenocrysts enclosed within a dark volcanic matrix. The leucite crystals appear light gray to whitish and locally weather slightly differently from the surrounding groundmass, allowing them to stand out prominently in the rock. Many crystals display rounded outlines, indicating partial resorption or magmatic corrosion during crystallization. However, unlike BH250-83b, the crystals do not show obvious thick reaction rims in hand sample or thin section. This suggests that although some minor resorption may have occurred, the crystals largely remained stable within the host melt. The matrix is dark gray and fine grained, consistent with rapid cooling of the remaining melt following crystallization of the larger leucite phenocrysts. The strong contrast between coarse phenocrysts and fine groundmass records a complex cooling history involving both slow deep crystallization and rapid final cooling. Porphyritic Texture BH250-83 is strongly porphyritic, with large leucite phenocrysts surrounded by a fine-grained volcanic groundmass. This texture indicates two major stages of crystallization: 1. Early slow cooling at depth allowed large leucite crystals to form. 2. Later rapid cooling of the erupted or shallowly emplaced magma produced the fine-grained matrix. The large size of the leucite phenocrysts suggests that leucite was one of the earliest major phases to crystallize from the magma. Groundmass Texture The groundmass contains: • tiny feldspar laths, • pyroxene microlites, • oxides, • and fine interstitial material. Many of the feldspar microlites show weak alignment, suggesting magmatic flow during emplacement. The overall texture resembles trachytic or pilotaxitic volcanic groundmass textures commonly observed in alkaline volcanic rocks. Optical Mineralogy of Leucite The thin sections of BH250-83 contain some of the most beautiful examples of leucite optical behavior preserved in the BH250 collection. Under plane-polarized light, the leucite crystals appear mostly colorless with low relief and contain numerous fractures, inclusions, and internal alteration domains. Some crystals contain trails of tiny opaque inclusions or minute melt inclusions concentrated along fractures and internal zones. Under crossed polarizers, the leucite displays the classic pseudoisotropic behavior characteristic of cooled leucite. Instead of exhibiting bright interference colors, the crystals remain mostly dark gray to black while displaying intricate tartan-style twinning and faint patchy birefringence. The internal patterns form remarkable: • grid-like textures, • plaid twinning, • tartan twinning, • intersecting twin lamellae, • and domain structures. These textures are among the most diagnostic petrographic features of leucite. Crystallographic Phase Transition in Leucite One of the most important features preserved in BH250-83 is the crystallographic phase transition recorded within the leucite crystals. Leucite is unusual because its crystal structure changes as it cools, producing distinctive optical textures that are easily recognized in thin section. At high magmatic temperatures, leucite crystallizes in the cubic (isometric) crystal system. Minerals in the cubic system are optically isotropic, meaning they remain dark under crossed polarizers regardless of stage rotation. During this early stage of crystallization, leucite crystals would therefore have behaved as true isotropic minerals. As the magma cooled, however, the cubic structure of leucite became unstable. The mineral underwent a subsolidus phase transition into a lower-symmetry tetragonal, and in some cases orthorhombic, structure. Although the external crystal shape remained approximately the same, the internal atomic arrangement reorganized into numerous crystallographic domains separated by twin boundaries. This structural reorganization produced: • tartan or plaid-like twinning, • patchy extinction, • weak birefringence, • and pseudoisotropic optical behavior. The term pseudoisotropic refers to minerals that appear nearly isotropic under crossed polars even though they are technically anisotropic. In leucite, the birefringence produced during the low-temperature transition is extremely weak and distributed among many tiny twin domains. As a result, the crystal commonly remains mostly dark under crossed polars while displaying intricate grid-like internal textures. The spectacular tartan-style patterns visible in the photomicrographs of BH250-83 are therefore not primary magmatic growth features. Instead, they are subsolidus crystallographic textures formed during cooling as the leucite adjusted from a high-temperature cubic structure to a lower-symmetry form. These textures make BH250-83 an exceptional teaching specimen because they directly connect: • crystal symmetry, • phase transitions, • optical mineralogy, • and igneous cooling history. Few minerals demonstrate the relationship between crystallography and optical behavior as beautifully as leucite. Internal Fractures and Inclusion Trails Several leucite phenocrysts display extensive fracture systems and trails of tiny inclusions concentrated along fractures and internal domains. These features likely formed during cooling and contraction associated with the crystallographic phase transition. As the cubic lattice reorganized into lower-symmetry structures, internal stress developed within the crystals, generating fractures and twin boundaries. The fractures later served as pathways for: • fluids, • melt inclusions, • tiny oxides, • and minor alteration products. The inclusion-rich zones visible in plane-polarized light likely represent trapped late-stage magmatic fluids or minute opaque minerals concentrated along structural weaknesses. Equilibrium Crystallization One of the most important features of BH250-83 is the absence of strong reaction rims surrounding the leucite phenocrysts. This is petrologically significant because leucite commonly reacts with evolving silica-rich melt to produce alkali feldspar. If the melt becomes more silica rich during evolution, leucite becomes unstable and may develop: • reaction rims, • replacement textures, • pseudoleucite, • or alkali feldspar coronas. However, in BH250-83 the leucite crystals remain largely intact and sharply bounded. This strongly suggests that: • the melt remained silica undersaturated, • the magma retained alkaline chemistry, • and the leucite remained in equilibrium with the surrounding melt. This equilibrium relationship distinguishes BH250-83 from BH250-83b, where leucite crystals display reaction textures and disequilibrium features. Magmatic Interpretation BH250-83 likely crystallized from a potassium-rich alkaline magma generated in an extensional tectonic or intraplate volcanic setting associated with mantle-derived alkaline magmatism. The Roman Magmatic Province of Italy is famous for producing: • leucitites, • phonolites, • tephrites, • and other potassic volcanic rocks. These magmas are commonly enriched in: • potassium, • volatiles, • incompatible trace elements, • and alkalis. The abundance of leucite indicates that the magma remained strongly silica undersaturated throughout crystallization. Fractional crystallization produced the porphyritic texture, while rapid late-stage cooling preserved the fine-grained volcanic matrix. The preservation of pristine leucite phenocrysts without major reaction rims indicates relatively stable magmatic conditions and chemical equilibrium during cooling. Geological Importance BH250-83 is scientifically valuable because it preserves: • feldspathoid mineralogy, • crystallographic phase transitions, • pseudoisotropic optical behavior, • tartan twinning, • silica-undersaturated magmatism, • equilibrium crystallization, • and alkaline volcanic textures. The sample serves as an excellent teaching specimen for: • optical mineralogy, • igneous petrology, • crystallography, • volcanic textures, • and alkaline magma evolution. Few rocks demonstrate the connection between crystal symmetry and optical behavior as beautifully as leucite-bearing phonolites such as BH250-83. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-83. Geology Department sample # D-2.9. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and handsample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=edb024dc77944287806ced7a90bd11ac" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=edb024dc77944287806ced7a90bd11ac">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wajbLUYd7wPnou5LgpbMPtA01KPGl_c6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1rwwrXrIaVpNJsKCPVYoLvSDErc44aiMd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1CsgEmxqqzACGKvUbFkl0efWfPpmvyQkX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pxNETuoDb2-dZH11rgjIpQi_h-HDdLsQ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OLjCpM85g9Na2KTU5dKwWyOjP130xkDU/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1w_my33KWVlCTWVAFT3ja5HfQp_ZYlC6r/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1y7qN5FlXWgTapGtleFVPJ2hylZQyBh4M/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wHVEx5syX2PBpqE7QEhfUOuj6gq6Q0l2/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RyAIRmDb6hWjLcQoJyadqq5nCBiO-kkB/preview" allow="autoplay"></iframe> <iframe width="640" height="480" src="https://drive.google.com/file/d/1RVE0iH_ZwcO3WM2auPxumwRZVOcD-fK9/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Contributor An entity responsible for making contributions to the resource Bereket Haileab Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Bolsena Civita Casetllana, Itally alkaline volcanic rock basalt Bolsena Bolsena Civita Castellana Civita Castellana crystallographic phase transition cubic symmetry Cubic to tetragonal leucite Equilibrium crystallization Feldspathoid feldspathoid stability Grid twinning igneous intermediate Italy Italy geology leucite leucite phenocryst leucite phonolite. leucite stability Leucite twinning Leucitophyre orthorhombic symmetry Phase transition phonolite pilotaxitic texture Plagioclase plaid twinning porphyritic texture potassic volcanic rock potassium-rich magma Pseudo-isotropic behavior pseudoisotropic behavior Pseudoisotropic leucite pyroxene microlites Roman Magmatic Province silica-undersaturated magma Subsolidus transformation Tartan twinning tetragonal symmetry Trachytic Texture volcanic Zoned feldspars https://bereket-haileab.geology.sites.carleton.edu/files/original/15302892ec8c9b2a8830f7ece2000a94.jpg d8a35a8b6279b72a0079e90ecbc5228e https://bereket-haileab.geology.sites.carleton.edu/files/original/ca1fdf3f88e700c83397f4c12597e742.jpg 64bd0223d8381afb5db7d1404f27eab4 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-83b Subject The topic of the resource • Leucite-bearing alkaline volcanic rock • Leucitophyre • Leucite phonolite Description An account of the resource Major Minerals: leucite, orthoclase, volcanic glass Minor Minerals: mellite, augite, titanaugite, plagioclase Optics: leucite with reaction rim, titanagute with strong anamalous interference colors. Leucite with Orthoclase Reaction Rim A Remarkable Example of Disequilibrium Crystallization in an Alkaline Volcanic Rock BH250-83b is one of the most scientifically important and visually striking samples in the BH250 collection. The thin section preserves spectacular reaction rims surrounding euhedral leucite phenocrysts, providing direct petrographic evidence for disequilibrium crystallization and magma evolution in a silica-undersaturated alkaline volcanic system. The sample is especially valuable because it captures a mineral reaction in progress — a texture rarely preserved this clearly in teaching collections. This specimen was collected in Uganda by the late Frank Brown of the University of Utah, an influential geologist and mentor whose work contributed significantly to East African volcanology and stratigraphy. Although the original hand sample is no longer available, the thin sections preserve extraordinary petrographic detail and continue to serve as some of the best teaching material for reaction textures, phase equilibria, peritectic reactions, and alkaline magma evolution. BH250-83b has been used in classroom instruction, research presentations, and publications because the textures are exceptionally clear and pedagogically powerful. The sample is especially useful for demonstrating the relationship between mineral stability, magma chemistry, and phase diagrams. It is also personally meaningful because of its connection to Frank Brown and because the thin section has become widely recognized among petrologists and mineralogists. The rock formed from a potassium-rich alkaline magma deficient in silica. Under such conditions, feldspathoid minerals such as leucite crystallize instead of quartz. However, BH250-83b records a critical stage in magma evolution where the chemical environment began shifting toward higher silica activity, destabilizing the leucite and triggering reaction-rim formation. Large euhedral leucite phenocrysts dominate the thin section and occur within a fine-grained dark volcanic matrix. The leucite crystals are surrounded by conspicuous pale reaction rims interpreted as orthoclase formed through reaction between leucite and silica-bearing melt. The matrix consists of abundant microlites, volcanic glass, opaque oxides, and pyroxene crystals. Many of the pyroxenes display strong brown coloration in plane-polarized light and vivid anomalous interference colors under crossed polars, characteristic of titanium-rich augite (titanaugite). The groundmass texture suggests rapid cooling of a volatile-rich alkaline melt after emplacement or eruption. Petrographic Description The thin sections display abundant euhedral to subhedral leucite phenocrysts enclosed within a dark fine-grained volcanic groundmass. Many leucite crystals retain sharp crystal boundaries and polygonal outlines, indicating that they crystallized early and developed freely within the melt before later reaction processes began. The most remarkable feature is the presence of continuous reaction rims surrounding many of the leucite crystals. These rims appear pale and finely crystalline in plane-polarized light and form complete coronas around the leucite grains. Under crossed polarizers, the rims display optical behavior distinct from the leucite interiors and are interpreted as orthoclase produced during magmatic reaction. Some leucite crystals preserve internal fractures and inclusion trails, while others display classic pseudoisotropic behavior with faint internal twinning patterns visible under crossed polars. The leucite interiors commonly remain dark or weakly birefringent, preserving evidence of their cooling-related symmetry transition. The matrix is composed of: volcanic glass, pyroxene microlites, oxide grains, feldspar microlites, and fine interstitial material. The alignment of some elongate crystals suggests local magmatic flow within the still-mobile melt during final crystallization. Reaction Rim Texture BH250-83b is an extraordinary example of a reaction-rim texture formed through disequilibrium interaction between leucite and evolving magma. The reaction observed in the thin section can be simplified as: Leucite + SiO2 → Orthoclase or more specifically: KAlSi2 O6 + SiO2 → KAlSi3 O8 This reaction records the destabilization of leucite as silica activity increased in the surrounding melt. Leucite is stable only in strongly silica-undersaturated magmas. As the magma evolved chemically — either through fractional crystallization, magma mixing, contamination, or changing melt composition — the surrounding melt became relatively more silica rich. Under these new conditions, leucite was no longer stable and began reacting with the melt to form orthoclase along crystal margins. The orthoclase rims therefore represent reaction coronas produced during magmatic re-equilibration. This texture is exceptionally important because it captures a disequilibrium process frozen in time. The rims demonstrate that the magma chemistry changed after the leucite crystals had already formed. Disequilibrium Crystallization Unlike BH250-83, where leucite remained stable and preserved equilibrium relationships with the surrounding magma, BH250-83b records disequilibrium crystallization. The reaction rims indicate that: leucite crystallized early, the magma composition evolved afterward, silica activity increased, and the earlier leucite crystals became unstable. The magma therefore crossed a mineral stability boundary during cooling and differentiation. This makes BH250-83b a remarkable natural example of: changing mineral stability, reaction textures, and magmatic evolution. Few teaching samples preserve this transition so clearly. Peritectic Reaction and Phase Diagrams BH250-83b is especially valuable for teaching phase diagrams because the reaction rims preserve a real petrographic example of a peritectic-type reaction. In simplified petrologic terms, a peritectic reaction occurs when: an early mineral reacts with melt, producing a new mineral during cooling. In this case: leucite was the earlier mineral, silica-bearing melt reacted with it, and orthoclase formed as the reaction product. The sample therefore provides a direct petrographic bridge between: mineral textures, phase diagrams, eutectic/peritectic relationships, and magma evolution. Students can observe: the original mineral (leucite), the reaction boundary, and the newly formed mineral (orthoclase). This makes BH250-83b exceptionally effective for teaching: mineral stability fields, silica saturation, alkaline magma systems, and reaction relationships in igneous petrology. Pseudoisotropic Leucite Several leucite crystals display pseudoisotropic behavior under crossed polarizers. Although leucite originally crystallized in a high-temperature cubic form, cooling caused the crystals to transform into lower-symmetry structures. At high temperature: leucite crystallized in the cubic (isometric) crystal system. During cooling: the crystal structure reorganized into tetragonal or orthorhombic symmetry. This transition produced: faint birefringence, internal domain structures, tartan-style twinning, and pseudoisotropic optical behavior. Because the birefringence remains extremely weak and distributed among many crystallographic domains, the crystals often appear nearly isotropic under crossed polars even though they are technically anisotropic. The dark interiors visible in the crossed-polarized photomicrographs preserve this remarkable crystallographic behavior. Orthoclase Reaction Rim The orthoclase rims surrounding the leucite are among the most important features of the sample. These rims: preserve a mineral reaction front, document changing silica activity, record magmatic disequilibrium, and demonstrate phase-boundary crossing during cooling. The rims are interpreted as orthoclase because: they occur directly at the leucite boundary, they are optically distinct, and they match the expected reaction product from leucite destabilization. The rims effectively isolate the remaining leucite from the surrounding melt, preserving partially reacted crystal cores. This is a textbook-quality coronitic texture. Titanaugite and Anomalous Interference Colors Several pyroxene crystals in the matrix display vivid anomalous interference colors under crossed polarizers. These pyroxenes are interpreted as titanaugite, a titanium-rich variety of augite common in alkaline volcanic rocks. Titanaugite commonly contains elevated: titanium, iron, and aluminum. These elements strongly influence optical behavior. The unusual interference colors result from: intense absorption, strong pleochroism, and deviations from ideal birefringence behavior. This phenomenon is referred to as anomalous interference coloration. Instead of displaying the normal first- and second-order pyroxene colors expected under crossed polars, titanaugite may display: patchy colors, unusually bright interference hues, bronze tones, or muted anomalous coloration. These pyroxenes therefore provide another excellent teaching feature preserved in BH250-83b. Volcanic Matrix and Cooling History The groundmass is fine grained and locally glassy, indicating rapid cooling during the final stages of crystallization. The matrix contains: microlitic feldspar, pyroxene needles, volcanic glass, and oxides. The fine grain size contrasts sharply with the large leucite phenocrysts, recording a two-stage cooling history: slow crystallization of leucite at depth, followed by rapid cooling of the remaining magma. The preservation of glass suggests that parts of the melt quenched before complete crystallization could occur. Geologic Importance BH250-83b is one of the finest teaching examples of: reaction rims, disequilibrium crystallization, leucite instability, alkaline magma evolution, peritectic reactions, silica saturation changes, and phase-equilibria textures. The sample beautifully demonstrates how minerals respond dynamically to changing magmatic conditions. It is especially important because the texture directly links: petrography, crystallography, optical mineralogy, and phase diagrams. Few rocks preserve these relationships as clearly as BH250-83b. Educational Importance BH250-83b is an outstanding specimen for teaching: igneous petrology, optical mineralogy, alkaline magmatism, crystallization sequences, phase diagrams, reaction textures, peritectic reactions, feldspathoid stability, and disequilibrium processes. Students can directly observe: early crystal formation, magma evolution, mineral instability, and reaction-front development. The sample transforms abstract phase-diagram concepts into visible petrographic reality. BH250-83b has attracted attention beyond the classroom because the thin-section textures are exceptionally distinctive and scientifically important. Over the years, educators, researchers, and mineralogy enthusiasts have discovered images of this sample through the BH250 collection website and have used BH250-83b in teaching materials, lectures, and even publications discussing leucite reaction textures, alkaline volcanism, and phase equilibria. Although some uses occurred without formal permission or attribution, it is gratifying to know that this remarkable specimen has contributed to broader geological education and scientific communication. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Uganda Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-83b. Housed at Carleton College in Minnesota. Contributor An entity responsible for making contributions to the resource Bereket Haielab Frank H. Brown Type The nature or genre of the resource Thin section Creator An entity primarily responsible for making the resource Bereket Haileab Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=290bdf0c4783466c8a271fe27e4e7b48" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=290bdf0c4783466c8a271fe27e4e7b48">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bGnWPmINF1S9G9OtS71Kv35mLVszlaib/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1KsaPb16uADSCjYLRD_fyXGombfrXBZJx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Qxb0c7nMo9PlYQVltbjZHKg5O_Cn1UkP/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gfY4K-449WJlkw3mQXj1F0dbhei2quKG/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pK0JAKn0FgTwF7IIKi0tqtg2HFd5zzoK/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1CxfC62NZO8nBaoqyCirRfDG31bRtj-yf/preview" allow="autoplay"></iframe> alkali feldspar Alkali feldspar replacing leucite alkaline volcanic rock Anomalous interference colors anomalous optical behavior Augite coronitic texture cross-hatched twinning crystal glass interaction cubic leucite cubic to tetragonal transition Disequilibrium Crystallization East African Rift euhedral euhedral leucite eutectic relationships Feldspathoid feldspathoid instability Feldspathoid-bearing rock formation of orthoclase coronas or rims around leucite Grid twinning igneous igneous mineral reaction incongruent melting KAlSi₂O₆ - KAlSi₃O₈– SiO2 system leucite leucite alteration leucite and quartz leucite instability leucite phenocryst leucite phonolite leucite reaction rim leucite replacement leucite to orthoclase leucite–orthoclase–quartz system Leucitophyre magma evolution magmatic disequilibrium melilite Microlites mineral reaction mineral reaction texture orthoclase orthoclase corona orthoclase reaction rim orthorhombic leucite peritectic reaction peritectic systems peritectic/incongruent melting phase diagram phonolite Pleochroism porphyritic texture potassic alkaline magma pseudo-isotropic pseudo-isotropic texture pseudoisotropic Pseudoisotropic leucite reaction corona reaction rim reaction texture silica activity silica enrichment silica saturation silica-melt interaction silica-undersaturated silica-undersaturated magma Subsolidus transformation Tartan twinning tetragonal leucite Titanaugite Titanium-rich pyroxene two component systems Uganda volcanics https://bereket-haileab.geology.sites.carleton.edu/files/original/455114553b7e5ed66a5f54f8e23e0871.jpg e40252bdd232e41c8f5219712198023f https://bereket-haileab.geology.sites.carleton.edu/files/original/a6290d1f40b71a08cb4ef33852b91d58.jpg 4ef016a4fc224f76596e5081d907eb2f Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-84 Subject The topic of the resource Phonolite, Orendite, Orendite Wyominite, Lamproite Description An account of the resource Major Minerals: leucite Minor mineral: phlogopite, phengite, phengitic mica Leucite Hills, Wyoming is a geologically fascinating area situated within the Rock Springs Uplift of southwestern Wyoming. It is renowned for its rare, leucite-rich volcanic rocks. These rocks are composed predominantly of ultrapotassic volcanic lithologies, including leucitite a rock characterized by fine-grained to porphyritic textures and abundant leucite (KAlSi₂O₆). This sample is from the geology collection and it is the same as the Leucite Hills that were collected by Cameron Webb, Josh Zoellmer, and Anderson Cole class of 2014! For chemistry and additional photomicrographs see BH250-131s. Petrology and mineralogy: Leucite is the dominant feldspathoid mineral, commonly forming euhedral phenocrysts as well as fine grains within the groundmass. Phlogopite, a Ti-rich variety of mica, is widespread in some samples and appears as both groundmass flakes and phenocrysts. Nepheline occurs occasionally as an accessory feldspathoid mineral. Geochemistry: The rocks are ultrapotassic, with K₂O contents often exceeding 10 wt% (see tables in chemical analysis) and plot in the phonolite field on the TAS diagram. They are rich in alkali oxides (Na₂O + K₂O) and display elevated concentrations of Large Ion Lithophile Elements (LILE) such as K, Rb, and Ba as seen in the spider diagram/Rare Earth Plot. Mica Types: The primary micas found in Leucite Hills volcanic rocks are, phlogopite, including Ti-rich varieties, which are compositionally distinct. These micas occur as well-formed phenocrysts (up to several millimeters in size) and are mineralogically and chemically significant indicators of mantle metasomatism and magmatic conditions. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-84. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=704dd545e49c49cbbdf05d9340c3d1b1" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=704dd545e49c49cbbdf05d9340c3d1b1">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1X-P_Hq-xo4rip_fTFErcJo63PEQusj6F/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1EtcowyAySPu8l_5hQoo6BWB-XT0pLZ6X/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1mhFTzq1IC1u9uTa2W6aUWF9iE98NSq2v/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1G3bxuheDC3D_sjIQr--HJW1X1napBWnf/preview" allow="autoplay"></iframe> <iframe width="680" height="480" src="https://drive.google.com/file/d/1r8Ez3je-_OrMeeLO52TTx8f8mUzU728z/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Leucite Hills, Wyoming Same as BH250-131s Feldspathoid minerals Feldspathoid volcanic rocks High K₂O content igneous intermediate Lamproite leucite Leucite Hills Leucitite Orendite Phlogopite phonolite Ti-rich phlogopite Ultrapotassic composition Ultrapotassic volcanic rocks volcanic Wyoming volcanics Wyominite Zirkel Mesa https://bereket-haileab.geology.sites.carleton.edu/files/original/50673ece2e493c0178c8d98b7f13c49a.jpg 5cb1e37f969206904d4c18cc1e2297d6 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-85 Subject The topic of the resource Amygdaloidal, porphyritic basalt Description An account of the resource Major Minerals: Titanaugite (zoned and showing Carlsbad twinning) Plagioclase Minor Minerals: Analcime, Zeolites, Serpentine (alteration product of olivine), Oxides Optical Features: Titanaugite displays anomalous interference colors, compared to expected birefringence values. Note on Anomalous Interference Colors: Titanaugite contains significant titanium, which enhances pleochroic absorption. This strong absorption alters the behavior of light as it travels through the crystal, causing deviations from the typical interference colors expected from its birefringence. These anomalous interference colors are primarily due to intense pleochroism and absorption linked to titanium and iron content, a phenomenon known as anomalous interference coloration. Amygdules and amygdaloidal basalt: Vesicles in basalt filled with concentrically zoned secondary minerals are a striking result of post-eruption processes, recording interactions between fluids and solidified rock. Vesicles form when volatiles (e.g., H₂O, CO₂, SO₂) escape from magma during eruption. As lava cools rapidly, gas bubbles become trapped, leaving spherical or elongated cavities. After solidification, hydrothermal fluids or groundwater enter the basalt and deposit minerals inside the vesicles, a process known as amygdaloid formation. The infilled vesicles, called amygdules, contain secondary minerals. Amygdules are rounded, almond-shaped mineral deposits. These minerals often form concentric bands due to stepwise precipitation as fluid conditions change (e.g., temperature, pH, or chemistry). Early minerals coat the walls; later ones fill the center. Supersaturation of minerals like calcite or zeolites leads to layered deposition. Typical textures include: • Concentric banding – Alternating mineral layers • Botryoidal texture – Grape-like mineral masses • Zonation – Color or compositional variation from rim to core These features not only stand out visually but also reflect the history of fluid-rock interaction and may indicate low-grade metamorphism or hydrothermal alteration. Common secondary minerals include zeolites, analcime, calcite, chlorite, and quartz, each marking shifts in post-volcanic conditions. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Tahiti Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-85. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="480" src="https://drive.google.com/file/d/1__85xv4CXoFcSPA4p6kHVmCi-xg7b7N9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jyt0kBHSq85T-ynaSLlw5OQchTGnq8WS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PplLShZzgedDSsFRw-UFqQDYkG1pBU2x/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ccoQsNlB-5ZkV7Wh572VL39v0FHpYJ66/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hvO49dl_nUyN68EhPfxJxUtl6iYFDP9e/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1mYuqyf-0h2pT6HGu2A51PM-3HU-aOQdq/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Altered olivine Amygdaloidal basalt Amygdaloidal texture Amygdules Analcime Anomalous interference colors basalt Botryoidal texture Carlsbad twinning Concentric banding Groundmass High-Ti pyroxene hydrothermal fluids igneous mafic mafic volcanic rock Ocean island basalt (OIB) Optical zoning Oxide minerals Plagioclase Pleochroic titanaugite Porphyritic basalt porphyritic texture Pyroxene with anomalous interference colors Serpentine alteration Serpentinization Tahiti basalt Titanaugite Titaniferous phases Titanium-rich pyroxene vesicular basalt vesicular texture volcanic Volcanic rock Zeolite group minerals Zoned pyroxenes Zoned titanaugite https://bereket-haileab.geology.sites.carleton.edu/files/original/29bff2a298672044dc1ca1b27f746828.jpg 22e67de52eee8eb6885bae25e915c1a5 https://bereket-haileab.geology.sites.carleton.edu/files/original/97cd96ed92eecdd8e4328867c4340614.jpg 2f4dd692406cf422087c2027a164047e Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-86 Subject The topic of the resource Peralkaline phonolitic volcanic rock (phonolite) Description An account of the resource <p>BH250-86 and BH250-86b are striking porphyritic volcanic rocks from the Bearpaw Mountains of Montana and represent an unusual example of silica-undersaturated alkaline magmatism. These rocks belong to the Bearpaw Green Porphyry, a classic alkaline volcanic suite noted for its distinctive mineralogy and evolved magmatic chemistry.</p> <p>The hand samples display abundant light-colored rectangular to blocky phenocrysts set within a fine-grained greenish-gray groundmass. Many of the large crystals are pseudoleucites—pseudomorphic replacement textures formed after primary leucite crystals. In many alkaline volcanic systems, leucite becomes unstable during cooling or later alteration and is replaced by aggregates of nepheline and alkali feldspar while preserving the original crystal shape. These pseudoleucite textures are among the most diagnostic and visually distinctive features of the sample.</p> <p>The mineral assemblage is characteristic of peralkaline to mildly metaluminous phonolitic rocks and includes:</p> <p><strong>Major Minerals</strong></p> <ul> <li><strong>Nepheline</strong>&nbsp;— a feldspathoid mineral indicating a silica-undersaturated magma.</li> <li><strong>Aegirine</strong>&nbsp;— a sodium-rich clinopyroxene common in alkaline and peralkaline volcanic systems.</li> <li><strong>Riebeckite</strong>&nbsp;— a sodic amphibole further supporting strongly alkaline magmatic conditions.</li> <li><strong>Pseudo-leucite</strong>&nbsp;— alteration textures after original leucite phenocrysts, now replaced by nepheline and alkali feldspar.</li> </ul> <p><strong>Petrography</strong></p> <p>Thin sections reveal a complex volcanic groundmass composed of fine acicular and fibrous crystals surrounding larger phenocrysts. The groundmass commonly displays trachytic to pilotaxitic textures produced by aligned feldspathoid and feldspar microlites during lava flow and cooling.</p> <p>Large pseudoleucite crystals preserve sharp crystal outlines despite extensive internal replacement. Under plane-polarized light, many of these crystals appear cloudy and altered, whereas crossed polars reveal intricate mosaics of fine crystalline replacement textures. Some phenocrysts contain fractures, reaction rims, and alteration patches filled with secondary minerals.</p> <p>The groundmass contains abundant slender laths and needles of aegirine together with small sodic amphibole grains. The dark mafic phases are dispersed throughout the matrix and locally concentrated around larger pseudoleucite crystals. The abundance of sodium-rich mafic minerals strongly supports crystallization from an evolved alkaline magma enriched in Na, Fe, and volatile components.</p> <p>Several photomicrographs show fine radiating fibrous textures surrounding opaque or altered mineral cores. These textures likely formed during late-stage devitrification, hydrothermal alteration, or replacement reactions associated with cooling of the volcanic rock.</p> <p><strong>Petrogenesis</strong></p> <p>The Bearpaw Green Porphyry formed from highly evolved alkaline magma generated under silica-undersaturated conditions. Such magmas are commonly associated with continental intraplate magmatism, low degrees of partial melting, and mantle sources enriched in alkalis and incompatible trace elements.</p> <p>The presence of nepheline and pseudoleucite demonstrates that the magma crystallized in a system deficient in silica relative to feldspar stability. Instead of quartz and common feldspar assemblages typical of subalkaline volcanic rocks, the magma stabilized feldspathoids and sodium-rich ferromagnesian minerals.</p> <p>The REE pattern for BH250-86 displays strong light rare earth element (LREE) enrichment and elevated incompatible element concentrations, consistent with an evolved alkaline magma derived from an enriched mantle source. The relatively smooth chondrite-normalized REE trend suggests fractional crystallization played an important role during magma evolution, while the absence of a pronounced Eu anomaly indicates limited plagioclase fractionation compared to strongly evolved felsic magmatic systems.</p> <p><strong>Educational Value</strong></p> <p>BH250-86 is an exceptional teaching sample for demonstrating:</p> <ul> <li>Silica-undersaturated igneous systems</li> <li>Feldspathoid mineralogy</li> <li>Peralkaline volcanic rocks</li> <li>Pseudomorphism and mineral replacement textures</li> <li>Alkaline magma evolution</li> <li>REE enrichment in evolved magmatic systems</li> <li>Volcanic groundmass textures in thin section</li> </ul> <p>The sample provides students with an excellent opportunity to study mineralogical and geochemical evidence for unusual alkaline magmatism that differs substantially from more common calc-alkaline volcanic rocks.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1315588918&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Bearpaw Mountains, Montana, USA Nearby Geographic Feature: Bearpaw Mountains Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 86. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=db9261f02685456783e287376889e44c" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=db9261f02685456783e287376889e44c">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1L_hlGo1ZY3cZtyUuQXI_orXoSZ9jKjjB/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RH0Jpb9WYLK-TjPZ8ccTLRDVomqm8X4D/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19bQqYxd68zoZjN9Ru94Xg_-l9zN_YrrC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RFSzV13_kfwBm9cZ87JDquZiYHFBTXyP/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FNSyn2jZUaSqT63d9PhsCfSC_-A5flKN/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/16GAkry256Mq-6tdyjGXge-LZoMKnRHye/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/17VAkjtIRJaPKzv3EEri_HBAkDKnD7zhn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kj3C1oTVEOyyyRmY02T4k1lTxTLo2Dcn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-XftCHoliaJCA3fiLhyC4Otkmub8FzZu/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hfxZPKlusOMl7bw_a_bOqYPKaP8p0cP_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1MkoM-1XApxhnNuqiYcesMpL9I54h13h4/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1w1IPIfwvJj0nwVmLgiyx7uuN-wND5lWD/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hzjT8XRLAEfa0yWixguYVRUTM5G7CJLx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QStJYi7tThvCmcpGz2shPY0nyAXW8hde/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lhuT_26pj4Wb1bfhmZBPGKowhg3tM92v/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/104zvoLyIOLv7ndQ1CGHrQH8QejqkHHAk/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1K2cnt4ObLZf6BNizjFpkzp_d8ZB7xPed/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ThJ_Lc5iff7JElXpmjv8ieEWkhH1YB3R/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_kh13wESRxvM-d0qJf_FUi9KEGtguojX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/170PfZZxiuIs500lH6HtLM-9AtG1Fs0nV/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-86. Creator An entity primarily responsible for making the resource Bereket Haileab Aegirine alkali-rich magma alkaline igneous rocks Alkaline magmatism alkaline volcanism Bearpaw Green Porphyry Bearpaw Mountains Bearpaw Mountains geology devitrification textures Feldspathoid Feldspathoid minerals Feldspathoid-bearing rock igneous leucite replacement mafic Microlites microlitic texture Montana geology Nepheline nepheline phonolite Nepheline-bearing rock Peralkaline igneous rock peralkaline phonolite peralkaline rocks phonolite phonolitic porphyry phonolitic rock pilotaxitic texture porphyritic texture porphyritic volcanic rock porphyry pseudo-leucite Pseudoleucite alteration Pseudoleucite texture replacement texture Riebeckite silica undersaturated silica-undersaturated silica-undersaturated magma Sodic amphibole Sodic pyroxene Trachytic Texture volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/cff9f14d06c3931e05a65336d5b6d7c9.jpg 9a0869126958d7be23ef61ffa4daacba https://bereket-haileab.geology.sites.carleton.edu/files/original/72d5a3e96164cae48a16af6032821ecf.jpg 2f4dd692406cf422087c2027a164047e Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-86b Subject The topic of the resource Peralkaline phonolitic volcanic rock (phonolite) Bearpaw Green Porphyry Description An account of the resource BH250-86 and BH250-86b are striking porphyritic volcanic rocks from the Bearpaw Mountains of Montana and represent an unusual example of silica-undersaturated alkaline magmatism. These rocks belong to the Bearpaw Green Porphyry, a classic alkaline volcanic suite noted for its distinctive mineralogy and evolved magmatic chemistry. The hand samples display abundant light-colored rectangular to blocky phenocrysts set within a fine-grained greenish-gray groundmass. Many of the large crystals are pseudoleucites—pseudomorphic replacement textures formed after primary leucite crystals. In many alkaline volcanic systems, leucite becomes unstable during cooling or later alteration and is replaced by aggregates of nepheline and alkali feldspar while preserving the original crystal shape. These pseudoleucite textures are among the most diagnostic and visually distinctive features of the sample. The mineral assemblage is characteristic of peralkaline to mildly metaluminous phonolitic rocks and includes: Major Minerals • Nepheline — a feldspathoid mineral indicating a silica-undersaturated magma. • Aegirine — a sodium-rich clinopyroxene common in alkaline and peralkaline volcanic systems. • Riebeckite — a sodic amphibole further supporting strongly alkaline magmatic conditions. • Pseudo-leucite — alteration textures after original leucite phenocrysts, now replaced by nepheline and alkali feldspar. Petrography Thin sections reveal a complex volcanic groundmass composed of fine acicular and fibrous crystals surrounding larger phenocrysts. The groundmass commonly displays trachytic to pilotaxitic textures produced by aligned feldspathoid and feldspar microlites during lava flow and cooling. Large pseudoleucite crystals preserve sharp crystal outlines despite extensive internal replacement. Under plane-polarized light, many of these crystals appear cloudy and altered, whereas crossed polars reveal intricate mosaics of fine crystalline replacement textures. Some phenocrysts contain fractures, reaction rims, and alteration patches filled with secondary minerals. The groundmass contains abundant slender laths and needles of aegirine together with small sodic amphibole grains. The dark mafic phases are dispersed throughout the matrix and locally concentrated around larger pseudoleucite crystals. The abundance of sodium-rich mafic minerals strongly supports crystallization from an evolved alkaline magma enriched in Na, Fe, and volatile components. Several photomicrographs show fine radiating fibrous textures surrounding opaque or altered mineral cores. These textures likely formed during late-stage devitrification, hydrothermal alteration, or replacement reactions associated with cooling of the volcanic rock. Petrogenesis The Bearpaw Green Porphyry formed from highly evolved alkaline magma generated under silica-undersaturated conditions. Such magmas are commonly associated with continental intraplate magmatism, low degrees of partial melting, and mantle sources enriched in alkalis and incompatible trace elements. The presence of nepheline and pseudoleucite demonstrates that the magma crystallized in a system deficient in silica relative to feldspar stability. Instead of quartz and common feldspar assemblages typical of subalkaline volcanic rocks, the magma stabilized feldspathoids and sodium-rich ferromagnesian minerals. The REE pattern for BH250-86 displays strong light rare earth element (LREE) enrichment and elevated incompatible element concentrations, consistent with an evolved alkaline magma derived from an enriched mantle source. The relatively smooth chondrite-normalized REE trend suggests fractional crystallization played an important role during magma evolution, while the absence of a pronounced Eu anomaly indicates limited plagioclase fractionation compared to strongly evolved felsic magmatic systems. Educational Value BH250-86 and BH250-86b are exceptional teaching sample for demonstrating: • Silica-undersaturated igneous systems • Feldspathoid mineralogy • Peralkaline volcanic rocks • Pseudomorphism and mineral replacement textures • Alkaline magma evolution • REE enrichment in evolved magmatic systems • Volcanic groundmass textures in thin section The sample provides students with an excellent opportunity to study mineralogical and geochemical evidence for unusual alkaline magmatism that differs substantially from more common calc-alkaline volcanic rocks. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Bearpaw Mountains, Montana, USA Nearby Geographic Feature: Bearpaw Mountains Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 86b. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Creator An entity primarily responsible for making the resource Bereket Haileab Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=99e70d695022407e93c457e907e4332f" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=99e70d695022407e93c457e907e4332f">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1id5fqrswQF7s9rUvreY_lT45HRewY7Bc/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19kunVmCy4YD5_u48rj1On6m35ZNz6hlU/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Jpgh59fPgMP-6l24QOUFr8UFt8n37JJQ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_mMW3QPKIwb5Ec6kqEXDwKQBNwVboQqI/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1qBBQ3rWVHjuZEkkkb-9iSCmZgwocrhfY/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1qvCotNORr-Wzm9nEcOf4VRHHFehS4R3y/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IN6cRG9Ud9tUWA3gmBF_3S3Jl8WtJNhm/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1j8OsdaUiVSt-vFSmgTkzVMLT8VZWdXEW/preview" allow="autoplay"></iframe> Aegirine alkali-rich magma alkaline igneous rocks Alkaline magmatism alkaline volcanism Bearpaw Green Porphyry Bearpaw Mountains Bearpaw Mountains geology devitrification textures Feldspathoid Feldspathoid minerals Feldspathoid-bearing rock igneous leucite replacement mafic Microlites microlitic texture Montana geology Nepheline nepheline phonolite Nepheline-bearing rock Peralkaline igneous rock peralkaline phonolite peralkaline rocks phonolite phonolitic porphyry phonolitic rock pilotaxitic texture porphyritic texture porphyritic volcanic rock porphyry pseudo-leucite Pseudoleucite alteration Pseudoleucite texture replacement texture Riebeckite silica undersaturated silica-undersaturated silica-undersaturated magma Sodic amphibole Sodic pyroxene Trachytic Texture volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/5ef6577773d95eeaec59f35f9b3f89d8.jpg 0d9520e7fdb4d4522fe165043d6359ac https://bereket-haileab.geology.sites.carleton.edu/files/original/55a549d7ac54fdccdaa7d4c2eb69851e.jpg 733fa860070d76227cd62d3ea75df0ce Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-87 Subject The topic of the resource Komatiite with Spinifex Texture Description An account of the resource <p><strong>Major Minerals:</strong>&nbsp;olivine (forsteritic composition)<br /><strong>Minor Minerals:</strong>&nbsp;serpentine, iron oxides (magnetite)</p> <p><strong>Textures:</strong>&nbsp;spinifex texture, spinifex olivine, sheaf-like olivine aggregates, acicular olivine phenocrysts, olivine pseudomorphs</p> <p><strong>Alteration:</strong>&nbsp;extensive serpentinization of olivine and oxidation to magnetite</p> <p>BH250-87 is one of the most scientifically important and visually striking specimens in the BH250 Collection. This rock is a classic komatiite from the Archean greenstone belts of Ontario, Canada, and preserves exceptionally well-developed spinifex textures—one of the defining characteristics of ultramafic volcanic rocks formed on the early Earth. Komatiites are rare volcanic rocks composed primarily of magnesium-rich olivine and pyroxene and are interpreted to have formed from extremely high-temperature mantle-derived magmas during the Archean Eon, more than 2.5 billion years ago. Their occurrence provides direct evidence that Earth’s mantle was substantially hotter in the distant geologic past than it is today.</p> <p>Komatiitic magmas erupted at temperatures estimated to exceed 1600°C, considerably hotter than most modern basaltic lavas. These high eruption temperatures produced extremely fluid, low-viscosity lava flows capable of rapid turbulent movement across the Archean surface. Because of their high magnesium contents—commonly greater than 18 wt.% MgO and in some cases approaching 30 wt.%—komatiites crystallized abundant olivine directly from the melt. In modern Earth settings, mantle temperatures are generally too cool to generate true komatiitic magmas, making Archean komatiites important indicators of early mantle dynamics, mantle plume activity, and the thermal evolution of the planet.</p> <p>The most distinctive feature of BH250-87 is the spectacular preservation of spinifex texture. The hand sample displays long, bladed, skeletal crystals of olivine radiating in parallel to fan-shaped aggregates. These crystals resemble the sharp blades of Australian spinifex grass, from which the texture derives its name. Spinifex texture forms when rapidly cooled ultramafic magma becomes strongly undercooled near the upper portions of a lava flow. Under these conditions, olivine crystals grow extremely quickly along preferred crystallographic directions, producing elongate skeletal morphologies rather than equant grains. The texture records a remarkable imbalance between crystal growth rate and nucleation rate during cooling.</p> <p>In BH250-87, many of the original olivine crystals are now pseudomorphed by serpentine and iron oxides. Although the primary olivine has undergone extensive alteration, the original crystal morphology remains beautifully preserved. The reddish-brown weathered surfaces reflect oxidation of iron-bearing minerals and development of magnetite during hydrothermal alteration and serpentinization. This replacement process is common in komatiites because magnesium-rich olivine is highly susceptible to hydration reactions during low-temperature metamorphism and fluid interaction.</p> <p>The photomicrographs reveal intricate internal textures associated with altered olivine spinifex blades. Under plane-polarized light, the elongated crystals show mesh-like serpentinization textures and fine opaque oxide development along fractures and grain boundaries. Under crossed polars, the pseudomorphs preserve the original skeletal crystal outlines while exhibiting low-order interference colors characteristic of serpentine alteration products. Some blades occur as parallel arrays, whereas others form radiating sheaves, emphasizing the rapid crystallization environment of the original lava flow.</p> <p>The larger photomicrographs illustrate the classic spinifex arrangement particularly well. Long acicular crystals intersect at high angles, producing a dramatic quench texture rarely preserved so clearly in Archean volcanic rocks. The surrounding finer-grained matrix likely represents rapidly crystallized residual melt between early olivine blades. Such textures provide important evidence for cooling gradients within komatiitic lava flows, where the upper chilled zones cooled quickly while interior portions cooled more slowly.</p> <p>Komatiites such as BH250-87 are important not only for understanding early Earth volcanism but also for economic geology. Many komatiitic lava systems are associated with magmatic nickel–copper sulfide deposits because their high-temperature magmas were capable of efficiently scavenging metals from the mantle and surrounding crust. Archean komatiite belts in Canada, Australia, and South Africa remain globally important targets for nickel exploration.</p> <p>BH250-87 serves as an outstanding teaching specimen because it links petrology, mineralogy, volcanology, mantle geochemistry, and early Earth history in a single sample. Students can directly observe how cooling rate controls crystal morphology, how alteration preserves original igneous textures, and how Archean mantle processes differed fundamentally from those operating today. Together with related specimens BH250-161 from the same region and BH250-87b from Australia, this sample allows students to compare komatiitic textures and alteration styles from different Archean terranes around the world.</p> <p><strong>Geological Significance of Komatiites</strong></p> <p>Komatiites are among the best evidence for a hotter Archean mantle and vigorous early mantle convection. Their existence suggests mantle potential temperatures significantly higher than modern values, likely associated with mantle plumes rising from deep within the Earth. Because komatiitic magmas are extremely magnesium-rich and fluid, they provide valuable constraints on mantle melting conditions, magma transport, and crustal growth during Earth’s earliest history.</p> <p>Today, true komatiitic eruptions are essentially absent from Earth’s surface, making preserved Archean komatiites invaluable records of ancient planetary processes. Rocks such as BH250-87 therefore represent more than unusual volcanic rocks—they are direct windows into the thermal and chemical evolution of the early Earth.<br /><br /></p> <p><strong>Additional Komatiite Specimens in the BH250 Collection</strong></p> <p>The BH250 Collection contains several important komatiite specimens that together provide an excellent comparative suite for studying Archean ultramafic volcanism, spinifex textures, alteration processes, and early mantle evolution. In addition to BH250-87 from Munro Township, Ontario, the collection also includes BH250-161 from the same Canadian komatiite sequence and BH250-87b from Australia. These specimens allow students to compare komatiites from two of the world’s classic Archean greenstone terranes.</p> <p><strong>BH250-161 — Komatiite, Munro Township, Ontario, Canada</strong></p> <p>BH250-161 is another komatiite specimen collected from the Munro Township area of Ontario, one of the most famous localities for Archean komatiites worldwide. Like BH250-87, this sample preserves spectacular spinifex textures formed by rapid crystallization of magnesium-rich olivine from extremely hot ultramafic lava. The specimen complements BH250-87 by showing variation in crystal size, alteration intensity, and preservation of primary igneous textures within the same volcanic sequence.</p> <p>The Munro komatiites are part of the Abitibi greenstone belt, one of the largest and best-preserved Archean volcanic provinces on Earth. These rocks formed approximately 2.7 billion years ago during a time when mantle temperatures were significantly higher than today. BH250-161 helps illustrate how cooling history and post-eruption alteration affected komatiitic lava flows differently within the same volcanic environment.</p> <p>In thin section, BH250-161 displays elongated skeletal olivine crystals and pseudomorphic replacement textures similar to those in BH250-87. Serpentinization, oxide formation, and localized recrystallization preserve evidence of both primary volcanic processes and later hydrothermal alteration. Together, BH250-87 and BH250-161 provide an outstanding teaching pair for discussing variability within komatiitic lava flows and the preservation of Archean ultramafic rocks.</p> <p><strong>BH250-87b — Komatiite, Australia</strong></p> <p>BH250-87b is a komatiite specimen from Australia, likely derived from one of the classic Archean greenstone belts of Western Australia, where some of the world’s best-preserved komatiitic sequences occur. Australian komatiites are globally significant because they preserve exceptionally well-developed spinifex textures and are closely associated with economically important nickel sulfide deposits. This sample was collected in Australia and generously donated to the BH250 Collection by John Goodge, Class of 1980.</p> <p>This specimen expands the geographic scope of the BH250 komatiite suite and allows direct comparison between Canadian and Australian Archean ultramafic volcanic systems. Although both formed from extremely hot magnesium-rich magmas, differences in metamorphic history, deformation, weathering, and alteration can produce noticeable differences in hand sample appearance and thin-section textures.</p> <p>BH250-87b displays classic bladed to acicular olivine spinifex textures with strong alteration to serpentine and iron oxides. The specimen demonstrates how original olivine crystal morphology can remain remarkably preserved even after extensive metamorphism and hydrothermal replacement. In some areas, radiating sheaf-like aggregates of olivine pseudomorphs create dramatic fan-shaped patterns characteristic of spinifex-textured komatiites.</p> <p>The Australian specimen is particularly valuable for teaching because it highlights the global distribution of Archean komatiitic volcanism and reinforces the interpretation that hotter mantle conditions were widespread during the Archean Eon. When examined alongside the Munro Township samples, students can compare mineralogy, crystal habit, alteration textures, and preservation styles between different Archean terranes.</p> <p><strong>Comparative Importance of the Komatiite Suite</strong></p> <p>Together, BH250-87, BH250-161, and BH250-87b form one of the strongest teaching groups within the BH250 Collection for illustrating:</p> <ul> <li>Archean mantle temperatures and early Earth volcanism</li> <li>Ultramafic lava compositions and high-Mg magmas</li> <li>Formation of spinifex textures through rapid crystal growth</li> <li>Olivine crystallization and skeletal crystal morphology</li> <li>Serpentinization and hydrothermal alteration of ultramafic rocks</li> <li>Greenstone belt geology and Archean tectonic environments</li> <li>Economic associations with nickel sulfide mineralization</li> <li>Variations in preservation between different Archean terranes</li> </ul> <p>These specimens collectively provide students with a rare opportunity to study true komatiites from two classic Archean localities and to directly observe textures that record some of the hottest volcanic eruptions in Earth history.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1894251494&amp;single=true&amp;widget=true&amp;headers=false"></iframe><br /><br />Click <a href="https://www.digitalscope.org/ViewerUI/?SlideId=dc001831-871c-457e-b02b-0bdafc7947ce">here</a> for a high resolution scan image done by digitalscope Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-87. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=d1c6033df1594befab6fe978f974942c" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=d1c6033df1594befab6fe978f974942c">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1qFSev510GPTw36s03d0HpFuytSgcYWFC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1eYOuK-WEg0wdXgMix9jXA0CAllFxwZjS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1r7T59sx5yKRh_LeV_swLMNqxUwc26OAC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/148kM010L7DM6YcwOIl15yn26cxtQSPmK/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Q1y6OPbYfvru6ywioOIlXjsdwyjk3Nim/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1GlfYxMRORUqcbcDGySggAYJtV3JPj2l1/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1MGoIEQuAWhSw4bfAF90y_NG66s1h56Qz/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1eIYH9_EKIc5JMaVoUCk-QwBWf0avAkdL/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1j85HVBxasYrlkNa-FtTAbJBVH7REgSZO/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1MGoIEQuAWhSw4bfAF90y_NG66s1h56Qz/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1yhlToLN8KU_RrFg6HabM8a-uqrVo3dT1/preview" allow="autoplay"></iframe><br />TAS diagram of BH250-87.<br /><br />Sample from komatiitic and iron-rich Tholeiitic lava #3, see articles <a href="https://drive.google.com/drive/folders/1HX9BT2xaZsnFomPviFUlSJg8rQpT1-nz" title="Pyke et al">a</a>, <a href="https://drive.google.com/drive/folders/1HX9BT2xaZsnFomPviFUlSJg8rQpT1-nz" title="Arndt et al, 1976">b</a> and <a href="https://drive.google.com/drive/folders/1s34d6E1bf9wQ2nlbzRK4ynhRU9vBMLuH" title="Rock suites, Department of Geology, Carleton College, Northfield Mn ">c</a> Creator An entity primarily responsible for making the resource Bereket Haileab Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Ontario Canada, Munro Township, ~ 48° 5'57.43"N, 81° 7'2.32"W Contributor An entity responsible for making contributions to the resource Bereket Haileab Abitibi Greenstone Belt Acicular olivine Archean craton Archean komatiite Archean volcanic rock Canada Early Earth volcanism forsterite Forsteritic composition Greenstone belt rock High-Mg volcanic rock igneous komatiite Magnetite (alteration product) Munro Township olivine Olivine phenocrysts Olivine to magnetite Olivine to serpentine Ontario Oxidation of olivine Oxide Pseudomorphs of olivine Serpentine (alteration product) Serpentinization Sheaf-like olivine Skeletal olivine Spinifex olivine Spinifex texture ultramafic Ultramafic chemistry Ultramafic Volcanic Rock volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/5ffd37027eb21e1d3f513cfdc97b7ce2.jpg 42f61b96377a08198104623a971a1129 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-87b Subject The topic of the resource Komatiite Description An account of the resource Major Minerals: olivine (forsteritic composition) Minor Minerals: serpentine, iron oxides (magnetite) Textures: spinifex texture, spinifex olivine, sheaf-like olivine aggregates, acicular olivine phenocrysts, olivine pseudomorphs Alteration: extensive serpentinization of olivine and oxidation to magnetite BH250-87b is a komatiite specimen from Australia, likely derived from one of the classic Archean greenstone belts of Western Australia, where some of the world’s best-preserved komatiitic sequences occur. Australian komatiites are globally significant because they preserve exceptionally well-developed spinifex textures and are closely associated with economically important nickel sulfide deposits. This sample was collected in Australia and generously donated to the BH250 Collection by John Goodge, Class of 1980. This specimen expands the geographic scope of the BH250 komatiite suite and allows direct comparison between Canadian and Australian Archean ultramafic volcanic systems. Although both formed from extremely hot magnesium-rich magmas, differences in metamorphic history, deformation, weathering, and alteration can produce noticeable differences in hand sample appearance and thin-section textures. BH250-87b displays classic bladed to acicular olivine spinifex textures with strong alteration to serpentine and iron oxides. The specimen demonstrates how original olivine crystal morphology can remain remarkably preserved even after extensive metamorphism and hydrothermal replacement. In some areas, radiating sheaf-like aggregates of olivine pseudomorphs create dramatic fan-shaped patterns characteristic of spinifex-textured komatiites. The Australian specimen is particularly valuable for teaching because it highlights the global distribution of Archean komatiitic volcanism and reinforces the interpretation that hotter mantle conditions were widespread during the Archean Eon. When examined alongside the Munro Township samples, students can compare mineralogy, crystal habit, alteration textures, and preservation styles between different Archean terranes. Comparative Importance of the Komatiite Suite Together, BH250-87, BH250-161, and BH250-87b form one of the strongest teaching groups within the BH250 Collection for illustrating: • Archean mantle temperatures and early Earth volcanism • Ultramafic lava compositions and high-Mg magmas • Formation of spinifex textures through rapid crystal growth • Olivine crystallization and skeletal crystal morphology • Serpentinization and hydrothermal alteration of ultramafic rocks • Greenstone belt geology and Archean tectonic environments • Economic associations with nickel sulfide mineralization • Variations in preservation between different Archean terranes These specimens collectively provide students with a rare opportunity to study true komatiites from two classic Archean localities and to directly observe textures that record some of the hottest volcanic eruptions in Earth history. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-87b. Housed at Carleton College in Minnesota. Contributor An entity responsible for making contributions to the resource Bereket Haileab John Goodge '80 Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=54e42610d4bf414fadae93f57ac0bbce" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=54e42610d4bf414fadae93f57ac0bbce">here</a><br /><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1eKdXSM7jibrbEpAS4tZzgZptyvG_BJdW/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1VoRJifo9iocqi39SJNaiL3Nos3TW3Kec/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1qdYLskf4NiC8z9s47V7Whjg4GZ2MLdx-/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-5dB-Fyd-hbTGz3-zK4KVHsnJnCpp9uH/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1uM8OUUF_nQvpNI2qZEZ7QBj8Ublh8cPS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ADjk29c3MthohW1VDeDpWbVmQopc_T_6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OitwXrA5o7ve2nc3wpur06oWj80ZPNI1/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PCfD0w2gANewHT99gDdPCk4o1L_89V94/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab John Goodge '80 Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Australia, collected by John Goodge '80 Ancient mantle melting Archean greenstone belt Archean volcanism Australia komatiite sample Early Earth mantle Forsteritic olivine High-temperature lava Iddingsite igneous komatiite Magnesium-rich lava Magnetite olivine Olivine alteration Olivine to iddingsite Olivine to magnetite Olivine to serpentine Serpentine spinifex Spinifex texture ultramafic Ultramafic Volcanic Rock volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/4223996deda127fe1e9f116169adec40.jpg defd0f891e46bafa7effc6383f47f3b8 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-89 Subject The topic of the resource Rhyolite ((Volcanic Companion to the Baxter Hollow Granite)) Description An account of the resource Major Minerals: sanidine, quartz, microcline, orthocalse and devitrified glass<br /><br />This Rhyolite is mapped as early Proterozoic, post-penokean in the <span><span>Observatory Hill and at Marquette (Baxter Hollow suite).<br /><br /></span></span>BH250-89 represents rhyolitic volcanic rocks exposed near the Baxter Hollow Granite in the Baraboo Range and helps complete the broader magmatic story that preceded deposition of the Baraboo Quartzite. These rhyolites are Paleoproterozoic in age and are generally associated with igneous activity that occurred approximately 1,760 – 1,830 Ma, broadly overlapping with emplacement of the Baxter Hollow Granite. Together, they represent felsic magmatism that affected southern Wisconsin during early Proterozoic crustal evolution along the margin of the Superior Craton. <p><span style="font-weight: 400;">The rhyolite and the Baxter Hollow Granite are likely related as volcanic-plutonic equivalents formed from similar felsic magmatic systems. The Baxter Hollow Granite crystallized slowly at depth, producing its coarse-grained phaneritic texture, while BH250-89 formed when chemically similar silica-rich magma erupted at or near Earth’s surface and cooled much more rapidly. In many Proterozoic terranes, rhyolites and granites occur together as part of large felsic magmatic provinces associated with continental arc magmatism, extensional magmatism, or post-orogenic magmatic activity. The Baraboo area preserves evidence of this broader igneous history in both intrusive and extrusive forms.</span></p> <p><span style="font-weight: 400;">Chemically, BH250-89 is silica-rich and dominated by quartz and feldspar components, with elevated potassium and sodium similar to many rhyolites. These rocks typically contain volcanic quartz, potassium feldspar, plagioclase, and minor biotite or iron oxides. In hand samples, rhyolite may appear pink, reddish, gray, or light tan depending on mineral content and oxidation history. Fine-grained groundmass dominates because the lava cooled rapidly, though phenocrysts of quartz or feldspar may be present if cooling occurred in multiple stages.</span></p> <p><span style="font-weight: 400;">Texturally, BH250-89 commonly exhibits an aphanitic to porphyritic texture, with fine-grained groundmass surrounding larger phenocrysts of quartz or feldspar. Some rhyolites in the region may also preserve flow banding, devitrification textures, or welded volcanic textures depending on eruption style. In the thin section, quartz phenocrysts may show embayed margins, while feldspars may exhibit alteration or deformation features related to later tectonic events. Similar to the Baxter Hollow Granite, the rhyolite may not appear strongly metamorphosed in outcrops, but microscopic examination can reveal subtle deformation effects such as recrystallization and mild undulose extinction in quartz grains related to later regional tectonism.</span></p> <p><span style="font-weight: 400;">These rhyolites likely contributed sediment to the developing Baraboo basin alongside the Baxter Hollow Granite. Once uplifted and exposed, both rock types underwent physical and chemical weathering. Feldspars altered to clays, unstable minerals broke down, and resistant quartz grains survived transport. Streams carried these sediments into coastal and shallow marine environments where repeated wave reworking concentrated exceptionally mature quartz sands that eventually became the Baraboo Quartzite.</span></p> <p><span style="font-weight: 400;">The presence of both BH250-89 rhyolite and BH250-89b Baxter Hollow Granite tells an important regional story: before the Baraboo Quartzite became one of North America’s classic mature quartzites, an older volcanic-plutonic terrane had to form, uplift, weather, and erode. These rocks preserve the igneous roots of that story and provide a direct link between Proterozoic magmatism and the sedimentary evolution of the Baraboo basin.</span></p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=2034475208&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Baraboo, Wisconsin, USA GPS Location: near 43°34'21.12"N, 89°15'59.68"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-89. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=a0c08647bd6b45ca889827656254c17b" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=a0c08647bd6b45ca889827656254c17b">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1rME0MsEF1mY_k-DQNN9NlGf3LAyWKgKp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15P6Y7XGrISS-99RxYYr-G9DIaOnQA-r9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1cJWRAKa8Ii1nHOQtHtkXTdUGvdnesTLs/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1N0Kpl1BHuaHasZY2tNbWJJY9nNmdNyLm/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wDp3glvCp4mamyDNED-dnQ47ePxHe4kk/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1q8mhxw6m9zD50fFNiBLBB09vZKo76SJh/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1W4j25iGDo204-lZvPZc169T1FsuC0cdh/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1iVi_GxwgbocJayLSsmhhNCePd-NhfZD_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/18GhXlkLujzgcO9UWvJvRgiiboY7BK3qo/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1y8x1TB3p3CKBtRC8KgR7u7IhSFvnsbhI/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_YE1ZIoUfDfiMSk1CC_NF7LoT2CObRO0/preview" allow="autoplay"></iframe><br />TAS diagram of sample 89. Creator An entity primarily responsible for making the resource Bereket Haileab Contributor An entity responsible for making contributions to the resource Bereket Haileab Baraboo felsic igneous post-penokean proterozoic rhyolite volcanic Wisconsine https://bereket-haileab.geology.sites.carleton.edu/files/original/62c85998cd25f10692061c06d632eb1e.jpg 93ded0da55051e6091983ac6949c6546 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-90 Subject The topic of the resource Diorite Description An account of the resource <p data-start="0" data-end="80"><strong data-start="0" data-end="78">BH250-90 — Diorite (Quartz-Bearing Diorite / Transitional to Granodiorite)</strong></p> <p data-start="82" data-end="267"><strong data-start="82" data-end="101">Major Minerals:</strong> plagioclase (albite twinning visible), quartz, orthoclase, hornblende, biotite<br data-start="180" data-end="183" /><strong data-start="183" data-end="202">Minor Minerals:</strong> titanite, zircon, apatite, Fe-Ti oxides, sericite (alteration)</p> <p>BH250-90 is one of the best teaching examples of diorite in this collection because it works beautifully at multiple scales—from hand sample to thin section to geochemistry. The sample was collected from a quarry near<span>&nbsp;</span><strong data-start="582" data-end="611">Little Chicago, Minnesota</strong>, and like much of Minnesota’s diverse bedrock assemblage, it was likely transported and deposited by Pleistocene glaciation rather than representing bedrock exposed at its original emplacement site. This glacial history adds another layer of geological interest, reminding students that hand samples collected from quarries, roadcuts, and glacial deposits may not always reflect the local bedrock geology. In hand sample, the specimen displays the classic<span>&nbsp;</span><strong data-start="1068" data-end="1100">“salt-and-pepper” appearance</strong><span>&nbsp;that makes diorite such a recognizable intrusive igneous rock in introductory geology courses. Light-colored feldspar and quartz are intergrown with darker hornblende and biotite, producing a coarse-grained phaneritic texture that clearly indicates slow cooling beneath Earth’s surface. The crystals are large enough to be easily identified by students in hand sample, making this specimen an excellent introduction to plutonic textures and intermediate igneous compositions</span>.</p> <p data-start="993" data-end="2029">Chemically, BH250-90 confirms what students first observe visually. With <strong data-start="1066" data-end="1085">61.42 wt.% SiO₂</strong>, the rock falls within an <strong data-start="1112" data-end="1140">intermediate composition</strong>, though it sits near the boundary between classic diorite and more silica-rich granodioritic compositions. The relatively high <strong data-start="1268" data-end="1286">Al₂O₃ (16.57%)</strong>, moderate <strong data-start="1297" data-end="1312">CaO (5.01%)</strong>, <strong data-start="1314" data-end="1330">Na₂O (3.93%)</strong>, and lower <strong data-start="1342" data-end="1357">K₂O (2.01%)</strong>reflect abundant plagioclase feldspar as the dominant felsic phase. Meanwhile, <strong data-start="1437" data-end="1457">Fe₂O₃(T) (6.87%)</strong>, <strong data-start="1459" data-end="1474">MgO (2.41%)</strong>, and <strong data-start="1480" data-end="1496">TiO₂ (0.69%)</strong> record the contribution of hornblende, biotite, and oxide minerals. The presence of <strong data-start="1581" data-end="1595">210 ppm Zr</strong>, elevated <strong data-start="1606" data-end="1622">Ba (619 ppm)</strong>, and <strong data-start="1628" data-end="1644">Sr (529 ppm)</strong> is consistent with crystallization from a relatively evolved calc-alkaline magma that retained accessory zircon, titanite, and apatite. This chemistry makes the sample particularly useful for teaching students that igneous rock classification is not always perfectly rigid—this specimen visually resembles diorite, but chemically trends toward <strong data-start="1989" data-end="2028">quartz diorite or even granodiorite</strong>.</p> <p data-start="2031" data-end="2659">Under plane-polarized and cross-polarized light, the thin section reveals a classic hypidiomorphic granular texture. Large plagioclase crystals dominate the rock and show well-developed <strong data-start="2217" data-end="2250">polysynthetic albite twinning</strong>, making them ideal teaching examples for feldspar identification. Some feldspar grains show minor alteration to sericite along fractures and cleavage planes, recording late-stage hydrothermal alteration. Quartz occurs as interstitial anhedral grains with low first-order gray interference colors and lacks strong deformation features, suggesting the rock remained relatively undeformed after crystallization.</p> <p data-start="2661" data-end="3476">The mafic minerals are especially instructive. Hornblende displays moderate to strong pleochroism in plane-polarized light, ranging from greenish-brown to olive tones depending on orientation. Under crossed polars it exhibits moderate birefringence and characteristic amphibole cleavage intersections. Biotite appears as brown pleochroic flakes and shows bright second-order interference colors. Several photomicrographs beautifully capture the relationship between these mafic minerals and the surrounding feldspars. One particularly elegant feature is the presence of <strong data-start="3231" data-end="3285">small apatite inclusions enclosed within amphibole</strong>, an excellent example of mineral inclusion relationships and crystallization sequence. Students can use this texture to discuss which minerals formed early versus later during magma cooling.</p> <p data-start="3478" data-end="3945">Accessory minerals add another layer of petrographic interest. Titanite occurs as high-relief grains with bright interference colors, zircon appears as small accessory crystals, and opaque Fe-Ti oxides contribute to the darker mineral assemblage. These minerals provide excellent opportunities to discuss trace element partitioning during crystallization and why elements such as zirconium, phosphorus, and titanium become concentrated in late-stage accessory phases.</p> <p data-start="3947" data-end="4419" data-is-last-node="" data-is-only-node="">BH250-90 is an outstanding specimen because it bridges introductory and advanced teaching. Beginners immediately recognize its salt-and-pepper hand sample texture, intermediate students can identify minerals optically, and advanced petrology students can connect its mineralogy to whole-rock chemistry and magmatic evolution. It is a specimen that demonstrates how hand sample observations, petrography, and geochemistry all work together to tell a coherent igneous story.</p> <br /><br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1710241944&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Little Chicago, Minnesota, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-90. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=96dae91d9256400bb865c7303f320506" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=96dae91d9256400bb865c7303f320506">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pzCSVm-hgUmMbd9zgY-_PBWp3hqy_aW6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OlcPTjTX0rWnApvqkq1cyvspG3lX3Daq/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FjJdM2NyE2wo2pQoUFcIUEiiNuL6UiBx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19yd1at-_lWaskZiQceuyPM8rLhK4O1Ab/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QuLPRYmGr5dq7mbBryySMZiEwdQ6_eyJ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1VnnJod_Ecb69s3E745XFJAwHPqYLN9yj/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/177QLvv4x0CxMKt4o8Vbz3tJAQ9esrZY6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BsEG-ZU5wrHNs28V8Ih4RgB3_EQsNInW/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1p_UpXqotg9UGngb7xFzAgUwI_k3rFasb/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1sZZyDk3V4DKiUk_7B4PYPdkUelfFi2v5/preview" allow="autoplay"></iframe>&nbsp;&nbsp;<br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Kx_PT_cz8iNM25RnFiECuBwVclfUphvd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lWUqcYIGa-aIFoqYiOwh4o8u2EZqxPMN/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gXvDH1Y2vguoRNaT6BEv_mkSBoafJtpx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1oXA7W5fSkZWQGDZTLb6q1upWyn9iMP1X/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15_K8U9rEkg_jbZNxXvVEU9IvTWCINL1P/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xb5GMMAbT0zrtVJYsWWH9ff9ZPS7KYLJ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1uCDQlJ3XgFPKV6_btQJqTpRIZ6Y7Sn3X/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-90. Creator An entity primarily responsible for making the resource Bereket Haileab Accessory minerals Albite twinning Apatite Apatite in Amphibole Biotite Calc-Alkaline Magma Coarse-grained igneous rock Continental crust magmatism diorite Fe-Ti oxides Granodiorite Transition Hornblende igneous intermediate Intermediate composition Intermediate Igneous Rock Intermediate Magma Intrusive Rock Mineral inclusions orthoclase Phaneritic texture Plagioclase plutonic Plutonic Igneous Rock Quartz Quartz Diorite Salt and pepper texture sericite alteration Sphene (Titanite) Zircon https://bereket-haileab.geology.sites.carleton.edu/files/original/d6f436b7a5c5d0e3fe39b4aa39c3a834.jpg 521f7e88bd63953eb79f2c1b3e2ebad3 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-91 Subject The topic of the resource Granite Description An account of the resource Major Minerals: quartz, orthoclase, hornblende, albite, biotite Minor Minerals: chlorite, oxides BH250-91 is a granite sample collected from railroad gravel near Granite Falls, Minnesota, close to an open pit. Although found in gravel, it is likely out of context, having been mined from nearby outcrops. The sample is particularly valuable for teaching purposes due to the presence of biotite and hornblende—two pleochroic minerals with perfect cleavage that are often associated but distinguishable under the microscope. The biotite contains numerous zircon inclusions that exhibit radiation damage. Additionally, the orthoclase in the granite shows alteration to sericite or white mica, providing a clear example of feldspar weathering. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Granite Falls Railroad Quarry, Minnesota, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 91. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=8b7d3082e20449a48bfdca82cc8c534d" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=8b7d3082e20449a48bfdca82cc8c534d">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1h6mzHUHRXhaje13f9r5NFikwiwj3nlk7/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Ac4Wq3KbQ5w6QUZkDLpW_0en6Eq8Agly/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1It6W0vRUbQAGcARXihQJmaO8PsaJwbVN/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BJRiL0hTfwd1Px9fUeQvmeclDG_OfIcP/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Biotite felsic granite Granite Falls Hornblende igneous Minnesota Pleochroic Minerals plutonic Radiation damage sericite alteration White mica Zircon inclusions https://bereket-haileab.geology.sites.carleton.edu/files/original/fefd918074c0925ff54b30f0cc615128.jpg 1a0d604115ce231b3f65947b595eb34d Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-92 Subject The topic of the resource Graphic Granite Description An account of the resource BH250-92 — Graphic Granite Major Minerals: quartz, orthoclase Minor Minerals: muscovite BH250-92 is a beautiful example of graphic granite, one of the most visually striking igneous textures students encounter in mineralogy and petrology. In hand sample, large white potassium feldspar crystals host dark gray quartz intergrowths that form angular, wedge-shaped, and vermicular patterns resembling ancient cuneiform writing, hence the term graphic. This is not a separate rock type, but rather a distinctive texture most commonly found in granitic pegmatites and highly evolved felsic intrusive bodies. Your specimen is particularly useful because the texture is exceptionally well developed and easily visible even to introductory students, making it an ideal teaching sample. Graphic granite forms during the final stages of granitic magma crystallization, when only a small volume of residual melt remains. By this stage, most early-forming minerals such as plagioclase, biotite, amphibole, and other common granite minerals have already crystallized and removed many major elements from the magma. What remains is a silica-rich, potassium-rich, water-rich residual melt enriched in incompatible elements and volatiles such as H₂O, F, B, Li, and other trace constituents. These volatiles lower the viscosity of the melt and allow ions to diffuse rapidly, creating ideal conditions for unusual crystal growth textures. As cooling continues, the residual melt approaches the quartz–feldspar eutectic composition. At the eutectic point, quartz and potassium feldspar become stable at nearly the same temperature and begin crystallizing simultaneously. Rather than forming separate, independent crystals, both minerals grow together in an interlocking fashion. Quartz commonly develops wedge-shaped rods or vermicular blebs enclosed within the growing orthoclase crystal. This simultaneous growth produces the characteristic runic or script-like texture seen in BH250-92. For intro to geology-level students, this specimen is an excellent introduction to the idea that texture records cooling history. They can easily observe that this is very different from ordinary coarse-grained granite and begin asking why quartz appears to be “written” inside feldspar. It opens discussion about intrusive cooling, magma evolution, and pegmatites. For upper-level petrology students, BH250-92 becomes much more sophisticated. It provides an opportunity to discuss: • eutectic crystallization • residual melt evolution • volatile enrichment in granitic systems • diffusion-controlled crystal growth • pegmatite formation • simultaneous nucleation of mineral phases • disequilibrium versus equilibrium crystallization textures Some researchers have proposed that portions of graphic texture may also be enhanced by exsolution processes, where quartz separates from feldspar during late cooling. However, the dominant interpretation remains simultaneous crystallization near eutectic conditions. The minor muscovite present in this sample further supports crystallization from a late-stage evolved granitic melt because muscovite commonly forms in volatile-rich pegmatitic environments. In many systems, graphic granite may occur adjacent to even more evolved pegmatites containing tourmaline, beryl, spodumene, topaz, or rare-element minerals. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-92. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=554ae8287e3c45089c00f7a16f748e3c" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=554ae8287e3c45089c00f7a16f748e3c">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xS6iBZeQk28Z0D3Ri91iR3Fate5rV5qX/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PW9CJjcXgWPJ8A42xcanjxaEFp-VYUtj/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Ky7gUPWM8xH1FvHlmA9Ne-86of1xwsQo/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OgTWbyEy-05riMgdPfwcuy6O1av1E-nh/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1zWNGxbmW6Xd4o0eDWmfnm4QY7NYzpVMw/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Cuneiform Texture Eutectic crystallization felsic granite Granite Pegmatite Granitic Differentiation Graphic granite Graphic Texture igneous Late-Stage Magmatism muscovite orthoclase Pegmatite Formation Pegmatite texture Pegmatitic Texture phase diagram Phase Equilibria plutonic Potassium Feldspar Quartz Quartz-Feldspar Eutectic Quartz-feldspar intergrowth Residual Melt Evolution Subject Graphic Granite Vermicular quartz Volatile-Rich Melt https://bereket-haileab.geology.sites.carleton.edu/files/original/62ff355fc836abb40086fc6149a9b55f.jpg e93195744475531a3440858ebe16d91f Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-93 Subject The topic of the resource Gabbro (Stillwater Complex, Montana) Description An account of the resource Major Minerals: Plagioclase, Diopside (clinopyroxene), Enstatite (orthopyroxene) Location: Stillwater Complex, Montana, USA BH250-93 is one of the best teaching samples in this collection for illustrating early plagioclase crystallization in mafic magma systems. Collected from the famous Stillwater Complex of Montana, this specimen represents a classic layered mafic intrusive environment where crystal settling, magma differentiation, and phase equilibria can be studied exceptionally well. The Stillwater Complex is one of the world’s best examples of a large layered mafic intrusion and is often compared to South Africa’s Bushveld Complex because both preserve remarkable records of magmatic differentiation. In thin section, BH250-93 displays a framework of interlocking euhedral plagioclase feldspar crystals that dominate the rock. These feldspars show well-developed crystal faces and clear polysynthetic twinning, indicating that they crystallized early when space was readily available within the magma chamber. The pyroxenes—both diopside (clinopyroxene) and enstatite (orthopyroxene)—occur primarily in interstitial spaces between the feldspar crystals and are noticeably more anhedral. Their irregular crystal boundaries indicate that they crystallized later, after much of the plagioclase framework had already formed. This textural relationship provides an elegant teaching example of a magma whose original composition likely began within the plagioclase primary crystallization field of a simplified plagioclase-pyroxene system. As cooling began, plagioclase nucleated first and grew freely, developing euhedral forms. The remaining melt gradually evolved toward eutectic conditions where both clinopyroxene and orthopyroxene began crystallizing in the remaining pore spaces. This sequence explains why the pyroxenes appear texturally constrained and anhedral. For introductory students, BH250-93 demonstrates how crystal shape reflects crystallization order. For advanced petrology students, it becomes an excellent exercise in reconstructing parental magma composition, equilibrium crystallization pathways, and interpreting simplified phase diagrams. This specimen beautifully demonstrates that texture can preserve the cooling history of a magma long after solidification. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Stillwater, Montana, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-93. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=47fc25b21fc74e57b9103369e37511ab" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=47fc25b21fc74e57b9103369e37511ab">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1VNOld-c1yL6lgAfTBCLZWZNLUgyUB3rc/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/17k2XgdZ2vMXibidp1Ku7YwqaIy-BHl6P/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OAicQi9JK9h7MxDpq5xHN4HC1N6rJ60O/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ywAyUihGAd53z8Q5SIyhJcbccnzLZFlr/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/11NgEnv0thJMC4Rp258O1PUgunwwp7cx3/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1S8HxaHDHzjm8CFiqpvQTU2TUL-mPv-OU/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Anhedral pyroxene Bowen’s Reaction Series Clinopyroxene Crystal Growth Sequence Cumulate texture Diopside Enstatite Equilibrium crystallization euhedral plagioclase Eutectic crystallization Fractional crystallization gabbro igneous Igneous Texture Interstitial pyroxene Interstitial Texture Layered Intrusions Layered mafic intrusion mafic Mafic Igneous Petrology Magma crystallization sequence Magmatic Differentiation Montana geology Orthopyroxene Phaneritic texture Phase diagram modeling Phase Equilibria Plagioclase Plagioclase-Pyroxene System plutonic Stillwater Complex Two-Component System