1 40 381 https://bereket-haileab.geology.sites.carleton.edu/files/original/dd032a82b62cffef71e152d0e158c962.jpg f0bfdcf1740ee7624fe2cfd7c10156e0 https://bereket-haileab.geology.sites.carleton.edu/files/original/90ff65076008377f4814de77960e1589.jpg 02aed0b04a41c237be87b3704ad6f6c6 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-1 Subject The topic of the resource Garnet–Sillimanite Schist (High-Grade Metamorphic Rock) Description An account of the resource Mineralogy Major Minerals: Sillimanite (including fibrolite) Garnet Quartz Minor Minerals: Muscovite Biotite Albite Orthoclase Zircon (accessory, often included in garnet) Texture & Fabric Strong foliation (schistosity) defined by aligned micas and fibrolitic sillimanite Slender prismatic and fibrous sillimanite forming mats and bundles Porphyroblastic texture with garnet crystals embedded in a foliated matrix Deformed garnets: flattened, elongated, and sometimes fractured Quartz inclusion-rich garnets, with trails recording earlier fabrics Growth zoning in garnets, indicating evolving metamorphic conditions BH250-1 is a striking example of a high-grade metamorphic rock that records both intense deformation and elevated temperature conditions deep within the continental crust. This rock is dominated by abundant sillimanite, occurring both as slender prismatic crystals and as fine fibrous aggregates known as fibrolite, intergrown with quartz and micas. One of the most distinctive features of this specimen is the presence of garnet porphyroblasts that have undergone significant deformation. While many garnets originally formed as euhedral, equant crystals, they are now commonly flattened, elongated, and stretched parallel to the rock’s foliation. In some cases, the foliation wraps through or even cuts across the garnets, indicating that deformation continued after or during garnet growth. This provides strong evidence for syn- to post-tectonic deformation. The garnets contain abundant quartz inclusions concentrated in their central cores, often arranged in trails or patterns that preserve earlier fabrics. In contrast, the outer rims of the garnets are largely inclusion-free, suggesting a later stage of crystal growth. These inclusion-rich cores are key to interpreting the rock’s history: They likely represent pre-existing foliation (S₁) that became trapped during early garnet growth. Their orientation relative to the external foliation helps reconstruct the rotational and deformational history of the porphyroblasts. The presence of inclusion-poor rims indicates that the garnets likely continued to grow after peak metamorphic conditions, during a later stage when deformation had diminished and fewer inclusions were incorporated. Many garnets also show growth zoning, reflecting changes in pressure–temperature–chemical conditions during crystallization. Taken together, the inclusion-rich cores and inclusion-free rims, along with zoning patterns, suggest that these garnets began forming as pre- to syn-tectonic porphyroblasts, and subsequently experienced post-peak (retrograde or late-stage) growth, followed by continued deformation that modified their overall shape and fabric. Metamorphic Interpretation This rock formed under upper amphibolite to granulite facies conditions, where temperatures are sufficiently high for the formation of sillimanite. Its mineral assemblage and textures indicate: High temperature metamorphism (sillimanite stability field) Likely moderate to high pressures typical of continental collision zones Prolonged deformation, resulting in: Rotation and flattening of garnets Development of strong foliation Overprinting of earlier mineral growth This combination suggests a tectonically active environment, such as a continental orogen, where rocks are buried, heated, deformed, and exhumed. In addition, the original bulk composition of this rock was clearly pelitic, as indicated by the abundance of sillimanite, muscovite, and plagioclase. This mineral assemblage is characteristic of aluminum-rich sedimentary protoliths (such as shale or mudstone), further supporting an origin tied to metamorphism of fine-grained sedimentary material under high-temperature conditions Geologic Significance BH250-1 is an excellent teaching example because it preserves a multi-stage metamorphic history: 1. Initial mineral growth (garnet porphyroblasts with inclusion trails) 2. Development of foliation and alignment of sillimanite and micas 3. Continued deformation, flattening garnets and modifying textures It clearly demonstrates how metamorphic rocks can act as records of both pressure–temperature conditions and deformation history, making it ideal for interpreting tectonic processes in deep crustal environments. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-1. Housed at Carleton College in Minnesota. Contributor An entity responsible for making contributions to the resource Bereket Haileab Carl Tape, '01 Type The nature or genre of the resource Thin section and hand sample 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: Alaska, USA Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=2681884ea4c4495fa3ec883c6366e7fb" 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=2681884ea4c4495fa3ec883c6366e7fb">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1V_mvQitTvu6rEifol4D4zNCyb8xgwNfU/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gC-CetpErmkVNkyrvdKP4RjFa6Z0yc2k/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1VM-IKcOzRFCQTOA6mDh33vKCTfHySwSh/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JuKBZ3vh3HK_oW8ha6cz-0Z7xtfhYT7t/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/18iXDSJMGTxZ-hR0dW10r1EDuLB83H3ze/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dfLPT8oawB5eV9RjOYnKINhJ3-tyYw73/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1mr_zzHj3cMwm9HDwFjA4rN3UJxOrmYBc/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bh0PjYlONnb_0E24xSXxObKcKUsPqIi9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Z0dbTA0qFiR_6Zq3bSXICY5LTiOgyG4g/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RUdwS0tfEGoZs_rqjVGd3BJrFuDkgVV9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1asq39_wTqq2TZCifrjETvNZ3fMexDrzR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BfrouU6DUC9DaavpK7nWMqF36OjlVJ-T/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1cNYTOqv67hi5csRzOMXmTBcfGi1DnBjV/preview" allow="autoplay"> <iframe src="https://drive.google.com/file/d/1GXZsfN3PoO-WPu_8bhu3jmP11rBmbKBP/preview" width="100%" height="480" allow="autoplay"></iframe></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RpH7h5Th7upV3gDrJGmXMoIwUztsQAFf/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1A21wyjClFmR5R1Y3BjywvREq0OX-iFex/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1855xR3LLdCSXry_BtjiElU-PlBzndVR1/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OOlhu6LVXxS7GWw9qsFE1ghKdvBDJsjn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1vqY6FVbTMaBL2lDVogvpaANsdmHKbn8R/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Alaska Geology Fibrolite Fibrous texture Garnet (Almandine) Growth Zoning Medium- to high-grade metamorphism metamorphic metamorphic rock Porphyroblasts Pre-Kinematic Garnet Pre-tectonic Garnet Prismatic Sillimanite Quartz Inclusions schist Schistosity sillimanite https://bereket-haileab.geology.sites.carleton.edu/files/original/767acb0d5f6fe328bbf43e682a2a01c5.jpg ac047440ccee8e066650aa587aeed880 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-10 Subject The topic of the resource Garnet Sillimanite Schist Description An account of the resource Major Minerals: garnet, sillimanite, quartz Minor Mineral: biotite, orthoclase, plagioclase Garnet sillimanite schist is a medium to high-grade metapelitic rock that forms under amphibolite to granulite facies metamorphic conditions. It is derived from aluminous shale or mudstone protoliths and reflects deep crustal metamorphism. In this sample, the major minerals are: Garnet – Large, porphyroblastic, now deformed Sillimanite – Typically occurs as fibrolite or prismatic needles Quartz – Forms the matrix and reflects metamorphic recrystallization Minor minerals: Biotite – Aligned in the foliation, contributes to schistosity Orthoclase and Plagioclase – Present as felsic phases, possibly from original sediment or late-stage metamorphic reaction Microstructure & Deformation: Porphyroblastic garnets are described as prograde and pre-kinematic they grew before the main deformation event and were subsequently deformed, suggesting syn- to post-tectonic strain after garnet crystallization. These garnets now exhibit strain shadows, pressure solution features, or boudinage, indicative of deformation during peak or retrograde metamorphism. Sillimanite are present as fibrolite along foliation planes, reflecting high-temperature metamorphism. Metamorphic Significance: The garnet + sillimanite + quartz ± feldspar assemblage places this rock within the upper amphibolite to granulite facies, and its mineralogy is consistent with pelitic bulk composition. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 10. 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=48dc06b1360c410fbc13ced065448ab3" 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=48dc06b1360c410fbc13ced065448ab3">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xcob7AzB2BmD7VBRYqKP1yztLbz7ck-R/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XYBPoibbVezQiVGHvBrAM4wf_XmpDpcR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZyyuLNVzsmzCH-_RtYbu08RfFu6BDlVb/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19IyP78jbyaG5B4RyOQqmkbQ_12KmaGAf/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1w_fVtBGuqIo3UV1yljMP62b56A2amykz/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1v3rhFuG6aGQTT-8Hzyzn_Ll9w1uwZ7Ns/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1stHfnCglJImTGfPBLBHNM44-OXOSlT6t/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Aluminous protolith Amphibolite Facies Fibrolite Garnet Garnet sillimanite schist granulite facies metamorphic Metapelite porphyroblastic Pre-Kinematic Garnet schist sillimanite https://bereket-haileab.geology.sites.carleton.edu/files/original/249b5a4b884335a2c3d53f7f92510c2f.JPG c65aaedf3566120810c39129ef72ea54 https://bereket-haileab.geology.sites.carleton.edu/files/original/6829fe66d5c3d3b7ea2dd8112662b453.jpg 1067444aa79e578d8e897c8ea991dbf0 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-100 Subject The topic of the resource Morton Gneiss Saprolite Description An account of the resource Major Mineral: quartz, sericite (white mica), kaolinite<br />Minor Minerals: iron oxides<br /><br /> <p>BH250-100 is a sample collected from the saprolite that formed from the chemical weathering of the Morton Gneiss near Redwood Falls, Minnesota.&nbsp;The Morton Gneiss is one of the oldest exposed rocks in North America. The saprolite represents a deeply weathered, in place alteration of this gneiss, and is primarily found in southwestern Minnesota. Despite its extensive chemical breakdown, the saprolite retains the foliation and mineral grain outlines of the parent gneiss as well as in the thin sections, preserving its original texture even as the rock has become soft, crumbly, and friable.</p> <p>The Morton saprolite typically appears reddish, orange, or buff in color due to the oxidation of iron-bearing minerals such as biotite. In both outcrop and hand sample, BH250-100 shows this distinctive weathered texture. Thin section analyses confirm that the primary mineral assemblage includes quartz, microcline, plagioclase feldspar, biotite, and garnet—typical of the Morton Gneiss. As weathering progresses, feldspar transforms into secondary minerals such as kaolinite and gibbsite, while biotite alters into iron oxides like hematite and goethite. Quartz, being more resistant, remains largely unaltered.</p> <p>Saprolitization of the Morton Gneiss likely occurred during the Late Cretaceous to early Paleogene, approximately 80 to 50 million years ago. In my course on the Geochemistry or Natural waters study, we attempted to use geochronology to more precisely date the weathering event by separating sericite/white mica from the sample and sending it for ^40Ar/^39Ar analysis. Although the argon retention in the sericite was insufficient for robust dating, preliminary results suggest a possible age of around 60 million years, consistent with other records of deep weathering during that time.</p> <p>The geochemical weathering process responsible for forming the saprolite from feldspar-bearing rock involves a well understood sequence of hydrolysis and leaching under warm, humid, and acidic conditions. The transformation of feldspar to gibbsite follows a multi-step pathway. Initially, hydrolysis of K-feldspar (orthoclase) produces potassium ions, dissolved silica, and secondary aluminum hydroxides:</p> <p>The alteration pathway commonly begins with the weathering of K-feldspar to muscovite (sericite) under conditions where potassium activity remains relatively high:</p> <p>KAlSi₃O₈ + H⁺ + H₂O → KAl₃Si₃O₁₀(OH)₂ + dissolved silica + K⁺</p> <p>With continued hydrolysis and leaching, feldspar alters to kaolinite under moderate silica activity and acidic conditions:</p> <p>2KAlSi₃O₈ + 2H⁺ + 9H₂O → Al₂Si₂O₅(OH)₄ + 2K⁺ + 4H₄SiO₄</p> <p>Under even more intense leaching, where potassium and silica are progressively removed from the system, kaolinite or feldspar may further alter to pyrophyllite in silica-rich but potassium-poor environments:</p> <p>Al₂Si₂O₅(OH)₄ + 2SiO₂ → Al₂Si₄O₁₀(OH)₂ + H₂O</p> <p>Finally, prolonged weathering and extreme silica depletion favor the formation of gibbsite, a highly aluminum-rich hydroxide mineral characteristic of advanced tropical or subtropical weathering profiles:</p> <p>Al₂Si₂O₅(OH)₄ + 5H₂O → 2Al(OH)₃ + 2H₄SiO₄</p> <p>The direct breakdown of feldspar to gibbsite may also be simplified as:</p> <p>2KAlSi₃O₈ + 2H⁺ + 9H₂O → 2Al(OH)₃ + 2K⁺ + 6H₄SiO₄</p> <p>These reactions illustrate the progressive loss of K⁺ and dissolved silica during weathering. As feldspar becomes unstable, secondary minerals evolve from K-bearing phases such as muscovite toward clay minerals such as kaolinite and eventually to aluminum hydroxides such as gibbsite.</p> <p>To better understand the conditions that allow this transformation, it's important to examine the relationship between&nbsp;pH&nbsp;and the&nbsp;log activity of potassium ions (log a_K⁺)&nbsp;in natural waters. This relationship is commonly visualized in&nbsp;pH – log(a_K⁺) stability diagrams. These diagrams illustrate mineral stability fields as functions of acidity (pH) and K⁺ concentration in solution. They help track the evolution of weathering processes by defining the stability domains of feldspar, kaolinite, and gibbsite. This is better explained in several textbooks especially the one by Drever "The Geochemistry of Natural Waters".</p> <p>In these diagrams, the x-axis represents&nbsp;pH, and the y-axis represents&nbsp;log(a_K⁺). At higher pH and K⁺ activity,&nbsp;K-feldspar is stable. As K⁺ is leached and pH decreases,&nbsp;kaolinite becomes stable. Under intense leaching and low K⁺ activity and acidic conditions (pH &lt; 5),&nbsp;gibbsite becomes the dominant stable phase.</p> <p>The weathering pathway observed in the Morton saprolite thus follows a trajectory from high pH and high K⁺ activity—where feldspar is stable—toward lower pH and depleted K⁺, stabilizing kaolinite and eventually gibbsite. This path reflects a progressive&nbsp;loss of K⁺ to groundwater, increasing&nbsp;silica leaching, and&nbsp;acidification by carbonic acid&nbsp;(from CO₂ in rainwater) or organic acids in the soil. The saprolite’s mineralogical transformation and geochemical context make it an excellent natural example of deep weathering in a continental craton environment.</p> <p>Chemical analyses of the un weathered Morton Gneiss (BH250-118) and the saprolite (BH250-100) reveal distinct geochemical signatures. BH250-118, representing the fresh rock, is enriched in silica, potassium (K), and sodium (Na), consistent with its original mineralogy dominated by feldspar and quartz. In contrast, the saprolite exhibits significantly lower concentrations of these elements, reflecting extensive leaching during chemical weathering. Elements such as K and Na are especially mobile in acidic, water-rich environments and are progressively removed from the weathering profile. On the other hand, relatively immobile elements particularly rare earth elements (REEs) are noticeably concentrated in the saprolite compared to the fresh Morton Gneiss. This enrichment results from the preferential removal of mobile elements, leaving behind a residual concentration of immobile components. See table and figures for comparative data.<br /><br /></p> <p>Several student research projects conducted in my Geochemistry of Natural Waters course focused on the sericite (white mica) present within the Redwood Falls saprolite. These studies examined the mineralogy, chemistry, and isotopic composition of the sericite in order to better understand the weathering history of the Morton Gneiss and the environmental conditions responsible for saprolite formation. Like to the papers can be found</p> <p>One student investigation used X-ray diffraction (XRD), scanning electron microscopy (SEM), electron microprobe analysis, Fourier-transform infrared spectroscopy (FTIR), and wavelength-dispersive spectroscopy (WDS) to characterize the white mica. The study demonstrated that the sericite is unusually depleted in potassium compared to typical muscovite or sericite compositions. Potassium concentrations measured by electron microprobe commonly ranged from only 0.04–0.11 wt.% K₂O, far below normal muscovite values of approximately 8–11 wt.% K₂O. This extreme potassium depletion suggests that the sericite experienced prolonged or repeated weathering under conditions that strongly leached alkali elements from the weathering profile.</p> <p>SEM imaging of the sericite grains revealed delicate mica-sheet textures and layered crystal structures preserved despite extensive chemical alteration. XRD analyses confirmed the abundance of kaolinite within the saprolite, while FTIR spectra suggested that portions of the sericite structure may have been partially altered toward kaolinite-like compositions. These results support the interpretation that the Morton saprolite underwent progressive chemical weathering in which feldspars first altered to sericite and later evolved toward kaolinite and gibbsite under increasingly intense leaching conditions.</p> <p>Another student project investigated the oxygen isotope composition of the sericite grains in order to reconstruct the paleoenvironmental conditions associated with saprolitization. The sericite was carefully separated from the saprolite using grain-size separation, magnetic separation, heavy liquids, and hand-picking techniques prior to isotopic analysis by laser fluorination mass spectrometry. Measured δ¹⁸O values ranged from approximately 40‰ to 50‰ relative to SMOW. Although these unusually high values were interpreted cautiously because of possible analytical complications during fluorination, the work demonstrated the potential for secondary weathering minerals in the Morton saprolite to preserve isotopic evidence of ancient meteoric water interaction and paleoclimatic conditions.</p> <p>Together, these student projects transformed BH250-100 into an important teaching and research specimen within the BH250 Collection. The saprolite not only illustrates large-scale chemical weathering of Archean crystalline rocks, but also serves as an exceptional example of how mineralogical, geochemical, and isotopic methods can be integrated to investigate ancient weathering processes, elemental mobility, and paleoenvironments. The studies also provided students with hands-on experience in modern analytical techniques including SEM, XRD, FTIR, electron microprobe analysis, and stable isotope geochemistry. Copies of the student papers, abstracts, posters, and related research materials can be found linked near the bottom of this page.</p> <p><br /><br /></p> <iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1008396863&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: Redwood Falls, Minnesota, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-100. 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=48ba975df3704a01b846b5a49e4c69e4" 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=48ba975df3704a01b846b5a49e4c69e4">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1U39BTgmT1S9zAhZvEt3xf-3zdqqV8G3n/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kyGl67s8wMyqYK103VqUJVao4b8I96xO/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1SsgkK1Jb4z_wGerWPeysXcoLm1eTTDBi/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1DJ1FMvp2mSddI1VjKMcQWQ_bjhuLYeM0/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lkl60oXamKjkIQEihPc--6aNYB_wuq_3/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1k_UY6iGr_qWcBdKmirkSFOj-6WJPcZ11/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OItFCt9zhUu_tyPobUNyrBlpmrCSH4SM/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1NadfilTGa5YrKMWWzsPfaxT1w_VkTQi-/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1FHy8p7Y2S3QIDGfPCQgYlTy5LjvO-3tX/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1bD4xkklyf0aZQyNIcuEKp41_RLVsJtyd/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/17Cr8yeFden0gWsssWDQ-YSIEksWb3koP/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1vt1WU8VAuGBAeccDDc_lhFQwZ9qnxKSL/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hWQf5sCfZ7VoPNNtvP3mr_hBIGp-J2S2/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XWvcQi8t9mv1EYqi360VL7arB3naJk5q/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Deep Chemical Weathering Geochemical Weathering Gibbsite Goethite Hematite Kaolinite metamorphic Morton Gneiss Paleosaprolite Precambrian pyrophyllite Redwood Falls Minnesota saprolite Saprolitic Weathering Sericite https://bereket-haileab.geology.sites.carleton.edu/files/original/eb49132157b7131b0771a6a9c14fb4ba.jpg 2fd8d21224b01446d6ae81dbc5f3f08c 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-100b Subject The topic of the resource Morton Gneiss Saprolite Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-100b. 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="480" src="https://drive.google.com/file/d/1mOc2BS7Vg1m6E3b1yMYTA36A8wpAm_W_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gn8tlnjMrfYRa3ms8ldKvkxPcLitLf8x/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Nz_iUR2cawp-FhSC1WWcfyktbDeA1vsV/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1TDjHd3mnxS25TUm2aluHkq_s9f29vYgd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-hKYzkR74MwLYyRXzFfi3a03Tj64Hojz/preview" allow="autoplay"></iframe> Description An account of the resource The Morton Saprolite near Redwood Falls, Minnesota, formed through deep chemical weathering of the Precambrian Morton Gneiss, one of the oldest rock units on Earth. As the gneiss weathers, it produces a distinctive mineral assemblage including quartz, kaolinite, sericite (white mica), gibbsite, goethite, and hematite. Despite extensive mineralogical alteration, the saprolite preserves the original fabric and banding of the gneiss — a hallmark feature of saprolitic weathering. The weathered material is typically reddish to yellowish-brown, reflecting the abundance of iron oxides. This saprolite has been the subject of multiple geochemistry student research projects, particularly focusing on its mineralogy, weathering processes, and geochemical evolution. Documentation and findings from these student studies are available through resources linked on this website. Several student projects have explored this subject; please refer to the papers, abstracts, and posters available on the Geochemistry of Natural Waters website. For more discussion on the Morton Saprolite see BH250-100 Clay Mineral Clay Mineral Formation Deep Chemical Weathering Element Mobility Feldspar weathering Geochemical Weathering Gibbsite Goethite Hematite Hydrolysis Immobile Element Concentration Kaolinite Leaching metamorphic Minnesota Minnesota River Valley Morton Gneiss Paleosaprolite Potassium Loss Precambrian Rare Earth Element (REE) Enrichment Redwood Falls Redwood Falls Minnesota Regolith Residual Soil saprolite Saprolitic Weathering Sericite Sericite Separation Silica Depletion Southwestern Minnesota Weathered Gneiss White mica https://bereket-haileab.geology.sites.carleton.edu/files/original/2d6fff3a2442d2023e22e19a8283d43d.jpg 5b680cc4c7adac8ceb2d8ba9454d8b77 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-100c Subject The topic of the resource Morton Gneiss Saprolite Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 100c. 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="480" src="https://drive.google.com/file/d/1lK8eyzzs5OVRH2PMjHr0kgY881X0gf_4/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1zT67ROMJQ0o3yUTRcTbGAQnPBj8zJAoC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-giicKdg6v1WZUI5fW6TpvP68fpyVWrh/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1y3O4UVrhU8oxZ9YbAV3vMdnQ44jNn7Dr/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1l8Nu1UeKvcH0SjoL1LOFTC2ZDWyPsAKZ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JHmVGtuMN0V2BtDVJYFjqNPUBbTvSh0j/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10U8ZghFT95XCm7e0gwop5sPgUqh2rrxo/preview" allow="autoplay"></iframe> Description An account of the resource The Morton Saprolite near Redwood Falls, Minnesota, formed through deep chemical weathering of the Precambrian Morton Gneiss, one of the oldest rock units on Earth. As the gneiss weathers, it produces a distinctive mineral assemblage including quartz, kaolinite, sericite (white mica), gibbsite, goethite, and hematite. Despite extensive mineralogical alteration, the saprolite preserves the original fabric and banding of the gneiss a hallmark feature of saprolitic weathering. The weathered material is typically reddish to yellowish-brown, reflecting the abundance of iron oxides. This part of the sample is less weathered Morton Gneiss than BH250-100, 100b This saprolite has been the subject of multiple geochemistry student research projects, particularly focusing on its mineralogy, weathering processes, and geochemical evolution. Documentation and findings from these student studies are available through resources linked on this website. Several student projects have explored this subject; please refer to the papers, abstracts, and posters available on the Geochemistry of Natural Waters website. For more discussion on the Morton Saprolite see BH250-100 Clay Mineral Clay Mineral Formation Deep Chemical Weathering Element Mobility Feldspar weathering Geochemical Weathering Gibbsite Goethite Hematite Hydrolysis Immobile Element Concentration Kaolinite Leaching metamorphic Minnesota Minnesota River Valley Morton Gneiss Paleosaprolite Potassium Loss Precambrian Rare Earth Element (REE) Enrichment Redwood Falls Redwood Falls Minnesota Regolith Residual Soil saprolite Saprolitic Weathering Sericite Sericite Separation Silica Depletion Southwestern Minnesota Weathered Gneiss White mica https://bereket-haileab.geology.sites.carleton.edu/files/original/be4ce6d8c5b0126f7a4f471dee880c3a.jpg b94e1024127717980d446a9ff01641aa 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-100d Subject The topic of the resource Morton Gneiss Saprolite Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 100d. 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="480" src="https://drive.google.com/file/d/1ZUxIutARyFAutj7cLfjUADwYjZaJAL1r/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IYc9HMlN-M20cAl7T_nB8-5JwByv5w1f/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Ox7z5csyTdSPbYh-dTLiww7-lYF1gjfc/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fEzKQ0uju82UkN65RL4p6Rsc4C8VVFcE/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fJQOkrmVOFABWVQXad-IMgHJ7t9wNJVh/preview" allow="autoplay"></iframe> Description An account of the resource The Morton Saprolite near Redwood Falls, Minnesota, formed through deep chemical weathering of the Precambrian Morton Gneiss, one of the oldest rock units on Earth. As the gneiss weathers, it produces a distinctive mineral assemblage including quartz, kaolinite, sericite (white mica), gibbsite, goethite, and hematite. Despite extensive mineralogical alteration, the saprolite preserves the original fabric and banding of the gneiss — a hallmark feature of saprolitic weathering. The weathered material is typically reddish to yellowish-brown, reflecting the abundance of iron oxides. This saprolite has been the subject of multiple geochemistry student research projects, particularly focusing on its mineralogy, weathering processes, and geochemical evolution. Documentation and findings from these student studies are available through resources linked on this website. This rock/saprolite is the least weathered Morton Geniss. Several student projects have explored this subject; please refer to the papers, abstracts, and posters available on the Geochemistry of Natural Waters website. For more discussion on the Morton Saprolite see BH250-100 Clay Mineral Clay Mineral Formation Deep Chemical Weathering Element Mobility Feldspar weathering Geochemical Weathering Gibbsite Goethite Hematite Hydrolysis Immobile Element Concentration Kaolinite Leaching metamorphic Minnesota Minnesota River Valley Morton Gneiss Paleosaprolite Potassium Loss Precambrian Rare Earth Element (REE) Enrichment Redwood Falls Redwood Falls Minnesota Regolith Residual Soil saprolite Saprolitic Weathering Sericite Sericite Separation Silica Depletion Southwestern Minnesota Weathered Gneiss White mica https://bereket-haileab.geology.sites.carleton.edu/files/original/5fad95d87e08e1919c5d3caeaf3599d2.jpg 7fa404a830f4d5cbfa8717067a3bb0a1 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 BH250-101 Subject The topic of the resource Alta Stock Granodiorite Description An account of the resource Major Minerals: plagioclase, biotite, hornblende<br /><br /> <p data-start="97" data-end="289">The Alta Stock, located in Alta, Utah, is a well-known granodioritic intrusion notable for its role in regional Mesozoic magmatism, contact metamorphism, and hydrothermal skarn mineralization.</p> <p data-start="291" data-end="942">Geochemically, the stock ranges from intermediate to felsic composition (see table below). It intrudes Mississippian–Pennsylvanian carbonate and clastic sedimentary rocks, producing a prominent contact metamorphic aureole. Metamorphic assemblages within this aureole include periclase, pure forsteritic olivine, tremolite, talc, diopside, wollastonite, ludwigite, vesuvianite, and recrystallized calcite and dolomite. These assemblages reflect both high-temperature metamorphism and skarn-type alteration, especially in carbonate-rich units exposed to metal-bearing hydrothermal fluids. Hornfels facies also developed in surrounding sedimentary rocks.</p> <p data-start="944" data-end="1117" data-is-last-node="" data-is-only-node="">Additionally, the Alta Stock is spatially associated with mineralization in the Little Cottonwood mining district, hosting or occurring near historic silver-lead-zinc veins.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1229250826&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: Alta, Utah, USA Nearby Geographic Features: Alta Stock GPS Coordinates: 40°34'53.31"N, 111°36'58.20"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 101. 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=29d89ab9ac8c44c5921e8b1c0eb81a37" 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=29d89ab9ac8c44c5921e8b1c0eb81a37">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ckMCnAtkQg-P5hUAsek8QVNC29jXk3M-/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/12JASs859L_VJ2dilhwhO7c81yPCm05tR/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Lgneqn_qReIblmBYVQqxd9cAJ-6ARxf8/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dudMmtz36vJz1grZBj8nK_7HpWPvy-KF/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/12_O9HzGFxzqOnt4CPG_8IBoR9AqFwAdM/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bQ39apjJI-1uiXfGWEos66eemGGsvsb7/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xjbtf9SdzVnPY3iOEoKvIWcyQoPKYxzF/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1MAZp6OLTHsjvxy2MrXGIXvVvMlOgIo5M/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-101. Creator An entity primarily responsible for making the resource Bereket Haileab Alta stock Carbonate Replacement contact metamorphism Diopside felsic granodiorite Hornfels Facies Hydrothermal alteration igneous Little Cottonwood Mining District Ludwigite Metamorphic Aureole Ore Deposits Periclase plutonic Silver-Lead-Zinc Veins skarn Skarn Formation Talc Thermal Metamorphism Tremolite Vesuvianite Wasatch Mountains Wollastonite https://bereket-haileab.geology.sites.carleton.edu/files/original/9c1357348c37f856e436d16ab530683b.jpg 8429c5c898643774b07f3b884185ed21 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-102 Subject The topic of the resource Periclase Bearing Marble Description An account of the resource Major Minerals: Periclase, forsterite (olivine), brucite, serpentine, calcite Alteration: Periclase alters to brucite; forsterite (olivine) alters to serpentine. Optical Properties: Periclase is a high-relief, isotropic mineral. In thin section, it is easily recognized by its high relief (n = 1.736), isotropic character (remaining dark in all orientations under crossed polars), and equant grain shapes. Periclase is susceptible to alteration during water-rock interaction, leading to the formation of brucite. In thin section, brucite is identified by its moderate birefringence, low relief, and fibrous habit. Altered periclase grains are often preserved as cores within brucite crystals. There are small amounts of forsterite associated with periclase in the periclase zone. The occurrence of forsterite in this zone of the Alta Stock metamorphic aureole reflects the local bulk composition of the protolith and specific metamorphic reactions that occur under the high-temperature, low- to moderate-pressure conditions typical of contact metamorphism. The periclase zone develops in Mg-rich, low-silica carbonate rocks (such as dolomitic marble) when subjected to high temperatures. Forsterite (Mg₂SiO₄) forms in this zone when small amounts of silica are present in the system, enabling the reaction: Dolomite + Quartz → Forsterite + Calcite + CO₂ 3CaMg(CO₃)₂ + SiO₂ → Mg₂SiO₄ + 3CaCO₃ + 3CO₂ This reaction requires silica (usually as quartz or introduced through fluid interaction, as siliceous dolomite), dolomite, and sufficient temperature. Texture: The metamorphic reaction that produces periclase is: Dolomite → Periclase + Calcite + CO₂. This means that in a sample that has undergone metamorphism, both calcite and dolomite may coexist. Since these two minerals have similar optical properties, distinguishing them requires careful observation. The following steps outline how to tell them apart: Recrystallized calcite and dolomite exhibit significantly larger grain sizes compared to the original unmetamorphosed siliceous dolostone. Both minerals display twin lamellae, a common textural feature in calcite and dolomite. In optical mineralogy, you can use the position of the relief change as you rotate the stage to identify the c-axis. Then, by using the Miller indices of the twin lamellae and examining the axial relationship between the c-axis and the twin lamellae, specifically whether the intersection forms an acute or obtuse angle, you can determine whether the carbonate mineral is calcite or dolomite. Rock Outcrop: This rock sample was collected adjacent to the Alta Stock granodiorite (BH250-101). The original rock was a siliceous dolomite. Contact metamorphism caused by the intrusion of the Alta Stock granodiorite metamorphosed the dolomite, recrystallizing it into a coarse-grained marble composed of calcite and dolomite. BH250-102, 102b and 102c are similar with the exception of 102c having larger forsterite (olivine) crystals. The outcrop is a popular destination for field trips and geology courses. Metamorphic Reactions: The likely metamorphic reactions leading to the formation of periclase and brucite are: Dolomite breakdown: Dolomite → Periclase + Calcite + Carbon dioxide CaMg(CO₃)₂ → MgO + CaCO₃ + CO₂ Hydration of periclase: Periclase + Water → Brucite MgO + H₂O → Mg(OH)₂ Simplified Alta Stock Metamorphic Progression: Talc Zone: Talc + dolomite Tremolite Zone: Tremolite + calcite/dolomite Forsterite Zone: Forsterite + calcite + diopside Periclase Zone: Periclase + calcite/dolomite 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: Alta, Utah, USA GPS Coordinates: 40°34'56.09"N, 111°36'40.74"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 102. 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=4219a4b1f41746a0a81b6e6f27ed1a6a" 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=4219a4b1f41746a0a81b6e6f27ed1a6a">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1NJqaLyPeiKE2TuUG4mQZ2QBUTPEcwXvi/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lrX66hKw1U5aSh7y9V3MZXX81mSFnLA-/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Crgg-CX38sYkJweMhQY_F3ZmENo1rf04/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1WVctXnRSAYwYqCnDSZE_whxS0nDDJ9Bq/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZjXnh0fFbRAxE7i0fxVjxNtj3aL6j_r-/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Lp6YfRsstcR41OVHlOV1iIrlWGcX1cZx/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Alta stock Alta Utah Brucite Calcite Recrystallization carbonate Carbonate Metamorphism contact metamorphism Dolomite Breakdown Isotropic minerals marble meta-carbonate metamorphic Olivine alteration Periclase Siliceous Dolostone https://bereket-haileab.geology.sites.carleton.edu/files/original/2666e7d1e8a2bdbb607528d7c827db14.jpg 5314628bab915f65b16016276992f690 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-102b (original Utah number 88-A5) Subject The topic of the resource Marble Description An account of the resource Major Minerals: Periclase, forsterite (olivine), brucite, serpentine, calcite Alteration: Periclase alters to brucite; olivine alters to serpentine. Optical Properties: Periclase is a high-relief, isotropic mineral. In thin section, it is easily recognized by its high relief (n = 1.736), isotropic character (remaining dark in all orientations under crossed polars), and equant grain shapes. Periclase is susceptible to alteration during water-rock interaction, leading to the formation of brucite. In thin section, brucite is identified by its moderate birefringence, low relief, and fibrous habit. Altered periclase grains are often preserved as cores within brucite crystals. There are small amounts of forsterite associated with periclase in the periclase zone. The occurrence of forsterite in this zone of the Alta Stock metamorphic aureole reflects the local bulk composition of the protolith and specific metamorphic reactions that occur under the high-temperature, low- to moderate-pressure conditions typical of contact metamorphism. The periclase zone develops in Mg-rich, low-silica carbonate rocks (such as dolomitic marble) when subjected to high temperatures. Forsterite (Mg₂SiO₄) forms in this zone when small amounts of silica are present in the system, enabling the reaction: Dolomite + Quartz → Forsterite + Calcite + CO₂ 3CaMg(CO₃)₂ + SiO₂ → Mg₂SiO₄ + 3CaCO₃ + 3CO₂ This reaction requires silica (usually as quartz or introduced through fluid interaction, as siliceous dolomite), dolomite, and sufficient temperature. Texture: Recrystallized calcite and dolomite are significantly larger in grain size compared to the original unmetamorphosed siliceous dolostone. Rock Outcrop: This rock sample was collected adjacent to the Alta Stock granodiorite (BH250-101). The original rock was a siliceous dolomite. Contact metamorphism caused by the intrusion of the Alta Stock granodiorite metamorphosed the dolomite, recrystallizing it into a coarse-grained marble composed of calcite and dolomite. BH250-102, 102b and 102c are similar with the exception of 102c having larger forsterite (olivine) crystals. The outcrop is a popular destination for field trips and geology courses. Metamorphic Reactions: The likely metamorphic reactions leading to the formation of periclase and brucite are: Dolomite breakdown: Dolomite → Periclase + Calcite + Carbon dioxide CaMg(CO₃)₂ → MgO + CaCO₃ + CO₂ Hydration of periclase: Periclase + Water → Brucite MgO + H₂O → Mg(OH)₂ Summary of Alta Stock Metamorphic Progression (simplified): Talc Zone: Talc + dolomite Tremolite Zone: Tremolite + calcite/dolomite Forsterite Zone: Forsterite + calcite + diopside Periclase Zone: Periclase + calcite/dolomite Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant GPS Coordinates: 40°34'54.57"N, 111°36'39.25"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 102b. 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=54b737d295db48e48057bb9bcd33c9db" 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=54b737d295db48e48057bb9bcd33c9db">here</a> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PztMmz2d45jb3SMgicf6zbrbxNv_SZk8/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1BccQWTG-L8SOjKpC7-E0qIwm-pN1JbBd/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1axN1WUCrHbQH8yRw7XwH_BEViJULChjw/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fjUcataiSZrD6LWq9uuVx4p4gCg1BObO/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1tBo_J-ZZ69LP3-zksbZfKAhj9744nEwQ/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1LLSnbOAzlB2YIYe6kmDtDa9rn9Cl73cv/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15vUx3qqugdsp6vRIGPqCuy1CLB5xGDOh/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1yagZGQWe-oR0_zK7YCbA00yEf1u2k2O7/preview" allow="autoplay"></iframe> carbonate marble meta-carbonate metamorphic https://bereket-haileab.geology.sites.carleton.edu/files/original/6919fae9dafbb1d2297c9d786bf77113.jpg 42e9a887d34affe52f834845d5b18d07 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-102c Subject The topic of the resource Periclase Bearing Marble Description An account of the resource Major Minerals: Periclase, forsterite (olivine), brucite, serpentine, calcite/dolomite Alteration: Periclase alters to brucite; forsterite (olivine) is altered to serpentine. Optical Properties: Periclase is a high-relief, isotropic mineral. In thin section, it is easily recognized by its high relief (n = 1.736), isotropic character (remaining dark in all orientations under crossed polars), and equant grain shapes. Periclase is susceptible to alteration during water-rock interaction, leading to the formation of brucite. In thin section, brucite is identified by its moderate birefringence, low relief, and fibrous habit. Altered periclase grains are often preserved as cores within brucite crystals. There are small amounts of forsterite associated with periclase in the periclase zone. The occurrence of forsterite in this zone of the Alta Stock metamorphic aureole reflects the local bulk composition of the protolith and specific metamorphic reactions that occur under the high-temperature, low- to moderate-pressure conditions typical of contact metamorphism. The periclase zone develops in Mg-rich, low-silica carbonate rocks (such as dolomitic marble) when subjected to high temperatures. Forsterite (Mg₂SiO₄) forms in this zone when small amounts of silica are present in the system, enabling the reaction: Dolomite + Quartz → Forsterite + Calcite + CO₂ 3CaMg(CO₃)₂ + SiO₂ → Mg₂SiO₄ + 3CaCO₃ + 3CO₂ This reaction requires silica (usually as quartz or introduced through fluid interaction, as siliceous dolomite), dolomite, and sufficient temperature. Texture: The metamorphic reaction that produces periclase is: Dolomite → Periclase + Calcite + CO₂. This means that in a sample that has undergone metamorphism, both calcite and dolomite may coexist. Since these two minerals have similar optical properties, distinguishing them requires careful observation. The following steps outline how to tell them apart: Recrystallized calcite and dolomite exhibit significantly larger grain sizes compared to the original unmetamorphosed siliceous dolostone. Both minerals display twin lamellae, a common textural feature in calcite and dolomite. In optical mineralogy, you can use the position of the relief change as you rotate the stage to identify the c-axis. Then, by using the Miller indices of the twin lamellae and examining the axial relationship between the c-axis and the twin lamellae, specifically whether the intersection forms an acute or obtuse angle, you can determine whether the carbonate mineral is calcite or dolomite. Rock Outcrop: This rock sample was collected adjacent to the granodiorite of Alta Stock (BH250-101). It shows strong alteration of periclase and olivine than BH250-102 and 102b. BH250-102, 102b and 102c are similar with the exception of 102c having larger forsterite (olivine) crystals. The outcrop is a common destination for field trips and geology field courses. Metamorphic Reactions: The likely metamorphic reactions leading to the formation of periclase and brucite are: Dolomite breakdown: Dolomite → Periclase + Calcite + Carbon dioxide CaMg(CO₃)₂ → MgO + CaCO₃ + CO₂ Hydration of periclase: Periclase + Water → Brucite MgO + H₂O → Mg(OH)₂ Summary of Alta Stock Metamorphic Progression (simplified): Talc Zone: Talc + dolomite Tremolite Zone: Tremolite + calcite/dolomite Forsterite Zone: Forsterite + calcite + diopside Periclase Zone: Periclase + calcite/dolomite Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant GPS Coordinates: 40°34'54.57"N, 111°36'39.25"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 102c. 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=46b2f6ba900d4104a4913d39cdd33ebb" 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=46b2f6ba900d4104a4913d39cdd33ebb">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wvb6vhwF-YtJLcmv2QKDhejCwDn-9WOv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1S87uUsC2ZU8mLsYO_v_VC_iw3qxmHjbp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1077gimNpH_C_rkGQdK9Bf_k8lmf337B9/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1L3YHbl6Q7-4msUvqOoJEm2nzL1JrEgS6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1lbvWzFu5B8ri3jBS91JbwFr1YNGXKQtC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1rgn01IeEMOJ6hTecIZwoQoABiSTHi3O4/preview" allow="autoplay"></iframe> carbonate marble meta-carbonate metamorphic https://bereket-haileab.geology.sites.carleton.edu/files/original/4a52ac0a72fcc630d3707329907a9db5.jpg 7f23764087ce2a9afcf19ab116fec08d 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-103 Subject The topic of the resource Forsterite Bearing Marble Description An account of the resource Major Minerals: Long prismatic altered forsterite, periclase, calcite, dolomite Sample BH250-103 is collected from the forsterite zone within the contact metamorphic aureole of the Alta Stock in Utah. This sample is mineralogically significant due to the presence of very long prismatic crystals of forsterite, which are now completely altered to serpentine. The pseudomorphic replacement preserves the original crystal habit of forsterite, making the alteration texture visually striking under the microscope. Additionally, periclase (MgO) is present in this sample as unaltered grains, along with some partially altered grains, especially when compared to the better-preserved periclase in the periclase zone of sample BH250-102. The alteration of periclase typically progresses to brucite (Mg(OH)₂) under retrograde metamorphic conditions. However, further petrographic or geochemical analysis would be required to confirm the specific alteration product present in this sample. The carbonate minerals, calcite and dolomite, occur as recrystallized grains displaying bimodal grain sizes: Very coarse-grained carbonates, which likely formed during the peak of contact metamorphism, Medium-grained carbonates, which may reflect recrystallization during retrograde metamorphism or subsequent hydrothermal fluid interactions. The coexistence of forsterite (altered to serpentine), periclase, and recrystallized carbonates reflects high-temperature, magnesium-rich skarn assemblages characteristic of contact metamorphism in carbonate protoliths. The textural relationships and mineral assemblage provide insights into the prograde and retrograde metamorphic history of the Alta Stock aureole. Summary of Alta Stock Metamorphic Progression (simplified): Talc Zone: Talc + dolomite Tremolite Zone: Tremolite + calcite/dolomite Forsterite Zone: Forsterite + calcite + diopside Periclase Zone: Periclase + calcite/dolomite 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: Alta, Utah, USA GPS Coordinates: 40°34'54.57"N, 111°36'39.25"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-103. 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=c0e3d6207fb44950955cac1503b0beaa" 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=c0e3d6207fb44950955cac1503b0beaa">here</a><br /><br /><iframe width="100%" height="480" iframe="" src="https://drive.google.com/file/d/12J8X3_fT4ionb6bWDhn39OnqbhTWVKTx/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1jnhQi3CiVDtU2MczmFE0yzARMIfE-7kQ/preview" allow="autoplay"></iframe> <iframe width="100%" height="100%" src="https://drive.google.com/file/d/1GfX51B9QFpd3bh1LdKO9WAAQrNvIOk_Y/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1fEamXcz3iCkXMdyaPiziwJotljV06DHR/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1X_TP1vtnPZRnmY-3ML-aRkCmRHgGGHU8/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1q0e0ERP7B6phVjhIJ79sE3wWIg5NKLqj/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1QfpIE3ziuODqNjlLQwiwUo1JiDSfw8tE/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1zJXlakJXjr62BcIuAQ_qAFwN9C22UPoC/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/101TrxNjsgeB-1YtazEODp8CWPnnkwUl2/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab John Bowman Alta stock calc-silicate carbonate Carbonate Protolith contact metamorphism forsterite Forsterite Zone marble metamorphic Metamorphic Aureole Mg olivine Periclase Prograde Metamorphism Recrystallized Carbonates Retrograde Metamorphism Serpentinization skarn Skarn Assemblage Utah https://bereket-haileab.geology.sites.carleton.edu/files/original/51e766245af92eb2d620ed0732b851e7.jpg 7b25295dcfa5079f4f58e6b3e01ebc94 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 Mineral Optics Gallery Subject The topic of the resource This collection contains minerals cut perpendicular to the c-axis in thin section. 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. Contributor An entity responsible for making contributions to the resource Bereket Haileab 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 BH250-103b Relation A related resource <iframe width="100%" height="480" src="https://drive.google.com/file/d/1sissQ7z0uutf5R64SEcNzze_OTUAdtSe/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dCSs984SXF2iKynuWgz_86d4e75Ev8TD/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bq8Cg1wuFB16YiN-lGzAUoiyJWQwW-Fp/preview" allow="autoplay"></iframe> Subject The topic of the resource Centered Opic Axis Figure Description An account of the resource BH250-103b (Marble, Alta, Utah) – Calcite interference figures Calcite in BH250-103b provides a realistic and instructive setting for learning interference figures because students must find the right grain rather than being given a perfect orientation. Begin in PPL and XPL by scanning the mosaic of recrystallized calcite for grains that are clean, inclusion-poor, and as equant as possible. Unlike ideal teaching sections, most grains will not be perfectly oriented. The goal is to identify grains that show very low birefringence at their center in XPL, often appearing nearly dark or with subdued first-order colors—an indication that you are looking close to the optic axis (c-axis) of this uniaxial mineral. Once a promising grain is located, center it carefully and switch to conoscopic observation. With proper alignment, calcite will produce a uniaxial optic axis figure, characterized by a centered melatope and a dark cross (isogyres) that remains centered during stage rotation. Because calcite has high birefringence, the isochromes are vivid and well developed, making the figure easy to interpret once the correct grain is found. Small rotations of the stage should keep the cross stable and centered, confirming that you are truly looking down the optic axis. In addition, BH250-103b contains grains that are slightly off the ideal orientation, producing off-centered optic axis figures where the melatope remains within the field of view but is displaced from the center. In these cases, part of the isogyre will sweep toward or out of the field during stage rotation—an important intermediate condition that helps students understand how figures evolve with orientation. To complete the analysis, insert the mica (sensitive tint) plate. Calcite is optically negative, so you should observe characteristic color changes in opposite quadrants of the figure that correspond to the fast and slow vibration directions. You can also use a quartz wedge test, where additional colors move toward the melatope in the addition quadrantsand move away from it in the subtraction quadrants, reinforcing the interpretation of vibration directions and optic sign. The key teaching value of BH250-103b is that students must work through the process—scanning, rejecting poorly oriented grains, and refining their choice—before obtaining a clean interference figure. This builds the skill of recognizing the right grain in a natural rock, which is far more transferable than working with idealized samples. BH250-36 (Single calcite crystal, c ⟂ section) – Reference standard Calcite in BH250-36 represents an idealized case: a single crystal cut perpendicular to the c-axis, meaning you are already looking directly down the optic axis. In XPL, the grain will show very low birefringence at the center, and in conoscopic view it produces a perfect uniaxial optic axis figure with a sharply centered cross and concentric isochromes. The figure remains fixed during stage rotation, providing a textbook example of a uniaxial interference figure. While BH250-36 is useful as a reference for what a “perfect” figure looks like, it removes the most important step in real petrographic work—finding the correct grain. For that reason, students should rely on BH250-103b to develop their observational skills and use BH250-36 primarily as a visual benchmark for comparison and confirmation. addition of retardation addition quadrants Bertrand lens birefringence birefringent mineral blue quadrants Calcite carbonate mineral centered optic axis figure chromatic bands concentric rings conoscopic illumination conoscopic image conoscopic interference pattern conoscopic observation dark cross (Maltese cross) fast ray direction first-order colors gypsum plate higher-order colors Interference Colors interference rings isochrons Isogyres length slow / length fast melatop Mica plate Michel-Lévy colors optic axis determination optical axis (c-axis) optical sign colors Optical sign determination optical sign test petrographic microscope Quartz Wedge retardation retardation colors slow ray direction subtraction of retardation subtraction quadrants Uniaxial interference figure uniaxial mineral Uniaxial negative vibration directions yellow quadrants https://bereket-haileab.geology.sites.carleton.edu/files/original/416086979a595cb64717efab3f161aa9.jpg 090193ba9c9e782a312c61ce9116530b https://bereket-haileab.geology.sites.carleton.edu/files/original/588d0afea726eb873f0e994a90766325.jpg 3db4ae9c4009c25e37bbb77b707f368c https://bereket-haileab.geology.sites.carleton.edu/files/original/89c5e4afc23bc2ac87a3ae4bd4ae94ff.jpg af2e26c470cb562ab92b236a96dc1f87 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-103b (Utah #88-C5) Description An account of the resource Major Minerals: Forsterite, periclase, calcite, dolomite Sample BH250-103b (Utah #88-C5) was collected from the forsterite zone of the contact metamorphic aureole surrounding the Alta Stock in Utah. This sample is mineralogically significant due to its abundance of coarser, unaltered, and notably elongate forsterite crystals. In hand sample, these forsterite grains stand out as prominent, white, and prismatic crystals that exhibit excellent preservation despite the high-temperature conditions of formation. Under the petrographic microscope, sections of forsterite cut perpendicular to the optic axis yield a straight-line isogyre in the interference figure, consistent with its biaxial optical character and a measured 2V angle of approximately 90 degrees. This diagnostic feature further confirms the identity and quality of the forsterite (100 % Mg endmember) in this sample. Associated carbonate minerals, predominantly calcite and dolomite, are present as large, recrystallized grains. Many of these grains are oriented such that they are nearly perpendicular to their c-axis, making them ideal for observing centered optic axis, off centered optic axis and really off centered optic axis interference figures in thin section. There are five videos that show these interference figures that you will find when you scroll down the page. This provides excellent teaching and reference material for demonstrating carbonate optical properties in mineralogy courses. When examining a mineral with high birefringence, such as calcite, the interference figure displays an isogyre surrounded by multiple isochromes centered around the melatope. By inserting the mica plate (also called a gypsum plate or accessory plate), colors in the interference figure will add or subtract in opposite quadrants. To determine the optic sign, look for the yellow color indicating subtraction. Connect the two quadrants showing yellow, extend an imaginary line between them, and align it with the known orientation of the mica plate’s fast ray. If this line forms a plus sign (+) with the fast ray of the plate, the mineral is optically positive. If it forms a minus sign (-), the mineral is optically negative. Alternatively, when using a quartz wedge on a microscope equipped for it, slowly insert the wedge while observing the interference figure. If the colors appear to move outward from the center of the figure (colors "flying out"), this indicates subtraction, meaning the mineral is optically negative. If the colors move inward toward the center ("flying in"), this indicates addition, meaning the mineral is optically positive. Compare the calcites in this thin sections to those in BH250-36. Periclase (un altered), another key phase in this sample, occurs as isotropic grains, though its presence is more limited compared to the silicates and carbonates. Overall, BH250-103b (Utah #88-C5) exemplifies the mineralogical and textural characteristics typical of high-temperature contact metamorphic marbles in the forsterite zone, preserving both the primary metamorphic assemblage and optical qualities that make it suitable for both research and educational purposes. These samples of BH250-102 to BH250-105 are definitely some of the best examples of contact metamorphism. Glad the Alta Stock area is not developed by developers and will stay that way so that future geologist will continue to visit and learn from this amazing place in the world. Summary of Alta Stock Metamorphic Progression (simplified): Talc Zone: Talc + dolomite Tremolite Zone: Tremolite + calcite/dolomite Forsterite Zone: Forsterite + calcite + diopside Periclase Zone: Periclase + calcite/dolomite Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-103b. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant GPS Coordinates: 40°34'54.57"N, 111°36'39.25"W 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=11c32512cd1e4a87a26565e11628000e" 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=11c32512cd1e4a87a26565e11628000e">here</a><br /><br /><iframe width="100%" height="480" iframe="" src="https://drive.google.com/file/d/1XEZZbm3HSKU9E8IBWj3CNZyEtau3p-6v/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gSwGCr0BpFD2FK_5_8WJzq4jleXslBPk/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1_Em6wRI4HwsiMBqyD6PbKz9sGHV1sFN-/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/17NZ2nLXfIXEkdslGEVrIbUoUIzP8nMCF/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1urmtYcTjO0zzsZ6-90Ay8ieb6b1H-JGY/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/12ErLEUpzGOhAy2xLpUWdqdUbWFTFZBCw/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1NRZ-dbircYy3GbuZLg2oFAUofjEYeWh3/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1sissQ7z0uutf5R64SEcNzze_OTUAdtSe/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1wXyBFLCG_r5bp7h_OprC6KK3HmNS_FNk/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1bq8Cg1wuFB16YiN-lGzAUoiyJWQwW-Fp/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/16spWBQHysuBl1NWZDA-xi1j96RKqhrZL/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1O8irfQuT2vaAOwKnlZqZLLoU7px1DmPR/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QF2VOsVoHiCc7cNifgSPZPKSN54MtZPH/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dCaBI0ntZxtBzvNEortc2MzanBrytRIR/preview" allow="autoplay"></iframe> Subject The topic of the resource Forsterite Bearing Marble 100% Mg-end member olivine 2V angle Addition Alta stock Biaxial Mineral Biaxial Optics calc-silicate Calcite carbonate Carbonate Protolith Carbonate Protolith Metamorphic Mineral Assemblage contact metamorphism Dolomite forsterite Forsterite (100% Mg-end member olivine) Forsterite Zone interference figure Isotropic mineral Magnesium-Rich Metamorphism marble metamorphic Metamorphic Aureole Mica Plate Test Periclase Prograde Metamorphism Quartz Wedge Test Recrystallized Carbonates skarn Skarn Assemblage Subtraction Uniaxial negative Uniaxial optics https://bereket-haileab.geology.sites.carleton.edu/files/original/aa78eb21d9b98674f08343e7508193e8.jpg e2a227e4d31258b9616bd981640afffe 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-103c (Utah #88-A9) Subject The topic of the resource Chondrodite and ludwigite Bearing Marble Description An account of the resource BH250-103C (Utah #88-A9) Major Minerals: Chondrodite (humite group), ludwigite, calcite, dolomite Sample BH250-103C (Utah #88-A9) was collected from the forsterite zone of the contact metamorphic aureole of the Alta Stock in Utah, but from a different locality than BH250-103 and BH250-103b. This sample is mineralogically significant for its abundance of coarse carbonate minerals, the presence of ludwigite, and smaller, nearly equigranular grains interpreted as chondrodite (of the humite group) rather than forsterite, which is more typical in other samples from the forsterite zone. The carbonate minerals, primarily calcite/dolomite, occur as recrystallized grains that include large, well-developed twinned crystals. The very coarse-grained carbonates likely formed during peak contact metamorphism. Notably, the calcite/dolomite crystals in BH250-103C (Utah #88-A9) are particularly well-suited for observing twin lamellae. This makes the sample valuable for optical mineralogy and petrographic studies, especially for: Differentiating between calcite and dolomite using Miller index geometry, Exploiting refractive index variations, Accurately locating the c-axis in carbonate crystals to determine whether you are looking at calcite or dolomite. In this sample, ludwigite is relatively common. Ludwigite is a boron-bearing magnesium-iron oxide mineral with the formula Mg₂FeBO₅, typically forming in contact metamorphosed, magnesium-rich carbonate rocks, particularly in magnesian skarns. It develops under high-temperature contact metamorphic conditions near igneous intrusions such as granite, granodiorite, or diorite stocks, as exemplified by the Alta Stock in Utah. The presence of ludwigite in this metamorphic aureole reflects boron enrichment introduced by metasomatic fluids, providing valuable insights into the fluid composition and metamorphic environment that governed skarn formation. Summary of Alta Stock Metamorphic Progression (simplified): Talc Zone: Talc + dolomite Tremolite Zone: Tremolite + calcite/dolomite Forsterite Zone: Forsterite + calcite + diopside Periclase Zone: Periclase + calcite/dolomite Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 103c. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant GPS Coordinates: 40°34'54.57"N, 111°36'39.25"W 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=541110c12f7e43ef86f9236d58cecd18" 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=541110c12f7e43ef86f9236d58cecd18">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1WAZqAPf44xe6i7vCkiJ9ttPSZLyZuwom/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ticGXf3px5aVSPZn6KJtroubEwGL76Jn/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1q4ydeDZEzny_5_tQiONp9MB7OFg3hxvW/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Wjy7GQXbw-SKkBb4pXtUp_HEUDDFt7Hm/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OfDoPc4O9PjdxmU7IbesZQl2TbYn93_P/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10KqLT2oT7ApVKGos997cSALUMppZBYaF/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jOKm7u3QhcoPQGc6xUgaU_7QM-kLRzBp/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XDGyGGh77rf4LlFDhS5oVqvZ93LJy-mr/preview" allow="autoplay"></iframe> calc-silicate carbonate marble metamorphic https://bereket-haileab.geology.sites.carleton.edu/files/original/91979fc224650b52449c6b7f218b8936.jpg b0cca9f97ba8a1f801da324a04ae6f4c 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-103d (originally BH250-4) Subject The topic of the resource Forsterite Bearing Marble Description An account of the resource Major Minerals: calcite, forsterite, altered microcline Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 103d. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant GPS Coordinates: 40°34'54.57"N, 111°36'39.25"W 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=c7a4fe94212146f88a6cf7452739ccfa" 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=c7a4fe94212146f88a6cf7452739ccfa">here</a> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kE6AICpI9Jq3WCkA-AE4WXpSigY1U6VF/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1qJa9SD8x6QEIx5-XqCguYWXlzfyMVTr3/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dVlf5Ae_REbuSoeI91v9qa478_GyFTtw/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/12mjYI97gIO9syCwdPmsc2ciMZ2FjTnRr/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1qYosasDndN0hM7ft71N6o0JMorASWpOr/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/173mE6OFMqgJ4GkLJU61ZqcL2uxu3fkey/preview" allow="autoplay"></iframe> calc-silicate carbonate marble metamorphic https://bereket-haileab.geology.sites.carleton.edu/files/original/21338a0631ec98e318c3171923eb36b2.jpg 98de870be5ac9b9d04a87774f48925e5 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-104 Subject The topic of the resource Tremolite Bearing Marble Description An account of the resource Major Mineral: Tremolite, calcite, dolomite In the contact metamorphic aureole of the Alta Stock, Utah, tremolite occurs within the tremolite zone, a distinct zone formed in carbonate-rich rocks, especially dolomitic marbles, due to the influence of the granodioritic intrusion. Tremolite develops in Mg- and Ca-rich dolomitic protoliths, typically alongside calcite, dolomite, diopside, and occasionally forsterite, depending on temperature and fluid availability. Its presence generally indicates lower to intermediate temperatures in the aureole, forming between the talc zone and the forsterite zone, before higher-temperature minerals like forsterite appear closer to the intrusion. Tremolite forms through the decarbonation of dolomite and quartz, producing CO₂ a key reaction in the contact metamorphism of carbonates. In thin section, tremolite is colorless to pale green, commonly prismatic or fibrous in habit. The metamorphic progression around the Alta Stock is typically: Talc Zone (talc + dolomite), Tremolite Zone (tremolite + calcite/dolomite), Forsterite Zone (forsterite + calcite + diopside), and Periclase Zone (periclase + calcite/dolomite). 5CaMg(CO3)2 + 8SiO2 + H2O = Ca2Mg5Si8O22(OH)2 + 3CaCO3 + 7CO2 Thus, tremolite serves as an important index mineral, marking the intermediate metamorphic grade and providing valuable insights into the metamorphic conditions and fluid evolution within the Alta Stock aureole. Within the tremolite-bearing zone, large calcite and dolomite crystals are present alongside tremolite. These carbonate minerals commonly exhibit well-developed twin lamellae and often display anomalous interference colors, rather than the typical high birefringence pastel colors expected of carbonates. This optical behavior makes them excellent candidates for obtaining centered optic axis interference figures in thin section studies. Rocks and Thin sections of BH250-104: Some thin sections show plenty of tremolite through the thin sections, however, older thin sections, you have to look hard to find the tremolite. Summary of Alta Stock Metamorphic Progression (simplified): Talc Zone: Talc + dolomite Tremolite Zone: Tremolite + calcite/dolomite Forsterite Zone: Forsterite + calcite + diopside Periclase Zone: Periclase + calcite/dolomite In summary, tremolite in the Alta Stock contact aureole is an important index mineral, representing an intermediate metamorphic grade in the progression from talc- to forsterite-bearing marbles, providing insight into metamorphic conditions and fluid interactions in the aureole. 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: Alta, Utah, USA GPS Coordinates: 40°34'48.68"N, 111°36'34.67"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 104. 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=60b0efda94444ccd8c98325bb808a9c8" 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=60b0efda94444ccd8c98325bb808a9c8">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wDwbaBFSf-KlFp2clh6hnU_ok1ZjVLzH/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FV43Uhtp8qEuCj-ZnSNgPncPqhQPouC6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/17ZnHlwa0fvVh7EWWXxvcUluCYd2KP-B6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dYr_2D2pb447r1HO-h4yYXUAilSSPnO6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1rOLXcpGs0RFwX1f2p1qt69l44j2H7jFG/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jtw8Upuq4S8eH26U7VEfZHszTQrkWNk1/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1CtZIumbkjuyCg_cy9yeYgF0VhyAp62ct/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PCPVMIP2jn0m89_o72TsS9JW81ex4m7b/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Oo4cYgjxcm7s7CxqhG9AB1U6LzCxTApf/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Alta stock Anomalous interference colors calc-silicate Calcite carbonate contact metamorphism Decarbonation Reaction Dolomite Index Mineral marble metamorphic Metamorphic Aureole Metamorphic Index Mineral Metamorphic Progression Optic Axis Interference Figure Tremolite Tremolite Zone Twin Lamellae https://bereket-haileab.geology.sites.carleton.edu/files/original/fb4dcda73462ee101e1d8e119c799a3d.jpg 5ea40a1dbce6af77b7831fe735e3f67d 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-105 Subject The topic of the resource Talc Bearing Marble Description An account of the resource Major Mineral: talc, calcite, dolomite Rock and Thin Section Description: This sample is from the outermost metamorphic zone of the Alta Stock aureole, approximately 4 km from the granodiorite contact. The talc and associated carbonate minerals are very fine-grained, making them challenging to identify without careful observation. In thin section, talc is present but requires close examination due to its subtle appearance and fine grain size. This zone corresponds to the talc zone, which marks the lowest-temperature conditions in the aureole's metamorphic gradient. It formed through the thermal metamorphism of Mg-rich, carbonate-bearing protoliths, particularly dolomitic marbles, under low-temperature, high-CO₂ conditions along the outer margin of the aureole. Occurrence and Formation: Talc typically forms via the reaction of dolomite and quartz in the presence of water, producing talc and releasing CO₂: 3Mg3CA(CO3)2 + 4SiO2 + H2O = 3CaCO3 + 3Mg3SiO4(OH)2 + 3CO2 Talc in the Alta Stock aureole represents the initial stage of thermal metamorphism, prior to the stabilization of higher-temperature minerals like tremolite, diopside, forsterite and periclase. Its occurrence is important for understanding the thermal gradient and fluid interactions across the metamorphic aureole and serves as a key index for mapping the extent of metamorphic influence from the intrusion. 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: Alta, Utah, USA GPS Coordinates: 40°34'35.81"N, 111°36'31.98"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-105. 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=4d4a89369888488db8a30e9a7d3e33a1" 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=4d4a89369888488db8a30e9a7d3e33a1">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/12kwUY7HVfvC-u5FRjSz3XrfK315iwEQ0/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OVNPDqmrAfG0og5yJXqmDgs1Iwrye42d/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1YA_29VA5Lmgz8MsSbEAUUIsqXkXskNMm/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_kBOXAk77GV-B1ikxToUhueDYnRPzH5P/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Alta stock Calcite contact metamorphism Decarbonation Reaction Dolomite Low-Temperature Metamorphism marble meta-carbonate metamorphic Metamorphic Aureole Metamorphic Index Mineral Talc Talc Zone Thermal Metamorphism https://bereket-haileab.geology.sites.carleton.edu/files/original/59971bd6e5b3806070a58659031b80a8.JPG 1be41e116d9e3f90d810ea278200d480 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 Sedimentary Rocks Subject The topic of the resource This collection includes sandstones, limestones, breccias, conglomerates, dolostones, shales, oolites, and BIF. 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. 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 BH250-106 Subject The topic of the resource Dolostone Description An account of the resource Major Mineral: dolomite This hand sample is from the un metamorphosed section of the rocks in Alta Utah. No thin section yet! 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: Alta, Utah, USA GPS Coordinates: 40°34'29.79"N, 111°36'30.56"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-106. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Hand sample Relation A related resource <iframe width="100%" height="480" src="https://drive.google.com/file/d/1yJDY8jy7l5--rLwkyIgnskVL1WJAW65D/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gFsSIiExJXzc0hpsXkFs6v-cqvXt3YWb/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab carbonate sedimentary https://bereket-haileab.geology.sites.carleton.edu/files/original/337f05f61275cfde9ddba490d259b6cd.jpg 8ad82094345cef736748c72d16e28cf8 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-107 Subject The topic of the resource Wollastonite Tremolite Skarn Description An account of the resource Major Minerals: wollastonite, tremolite, dolomite There is only 1 thin section with wollastonite. The rest of the thin sections contains mostly tremolite with few wollastonite . Check this out! 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: Alta, Utah, USA GPS <br />Coordinates: 40°34'38.71"N, 111°36'15.54"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-107. 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=d4c4f16df5724361b43dda0f1585fe02" 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=d4c4f16df5724361b43dda0f1585fe02">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14nFbrDfm3W0360TXpoqdhPKOw8nH6iz1/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1f7GQr_GfBBOcqpCJNbZZu9X-iSVtwFWl/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XImDRDEvoZsrISZG6LWzDfXrmnw3mARy/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1o_ytRZanhyNuKG7-90pYKAQvrCV_NAKZ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1d9rKz0z2H8xpC0IQ23jtYCGzQTgcf3kN/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1w747KDwPngy6ooDimje4m9Ho6E-M5EEa/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Y3GBw6wXbotGJ7OGIT4ETGIct9esTkn2/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JbuywTTO_M7RYDM7uyLFpQf2Vl6ihlvC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10zID8UwyvIRju-MZugtS6VFhMuUxRP55/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1WZvrdx42ydODk0xP81O6kdqx8hjli-cQ/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab metamorphic metasomatic skarn https://bereket-haileab.geology.sites.carleton.edu/files/original/234d6e764aeb7f48b25919b640156be1.jpg cc38fd23817e01b315726584cf082450 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 BH250-108 Subject The topic of the resource Obsidian Description An account of the resource Major Minerals: glass Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-108. 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=5ce36e114aff409f952233ad10c392e3" 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=5ce36e114aff409f952233ad10c392e3">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/114gWWvj9X04LoKRcim_4q5oBZmPLXIbY/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Ln3jX5M5YXcnqZoUxYi4QM7Dqy8PGU-Y/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1HOZAhYVvS8_2xTL5d-0JhoSeIOO6ZRow/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dLH1ZO0SAXtvb1_yLF4yNkRrWMlwB3Yv/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kcwJhVESwfPVdnZcmilnaYoSlvmo8y-_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1eHL0b851MexbCRDsG-hBjOq-Ivs0Shct/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab felsic igneous obsidian volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/7c60103ad052a5717c75dc13e1aad635.jpg 67ec6ee251de4c63f02a425f2698123b 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 Sedimentary Rocks Subject The topic of the resource This collection includes sandstones, limestones, breccias, conglomerates, dolostones, shales, oolites, and BIF. 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. 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 BH250-109 Subject The topic of the resource Tegate Limestone Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 109. 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="480" src="https://drive.google.com/file/d/1qlUop6Z57EhxX4xH92iTGUvs3m969v-Z/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1cKLJzn7yA87D6kIJRC6VF_WQco0CE_Uq/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1i8FgsOsEF8ljh6B1lmLCp6rK3qKu_wd7/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab carbonate limestone sedimentary 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/1966637e3d965f4fda4a527f9d9b16c4.jpg 9a426aaaf14f44777f66822c3b7f8c13 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-110 Subject The topic of the resource Garnet Biotite Schist Description An account of the resource Major Minerals: garnet, biotite, muscovite, plagioclase, quartz Schistosity: Well-developed foliation due to the alignment of biotite and muscovite. Porphyroblastic Texture: Garnets occur as porphyroblasts, growing large amidst a finer-grained matrix with quartz inclusions. 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: Black Hills, South Dakota, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-110. 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=4bf8e0a4088b4335ab0df27a00684a8b" 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=4bf8e0a4088b4335ab0df27a00684a8b">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1McA_r6HjdIl4k9sqd14JCMECVg5aD6dM/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ENHtWLRBT4r7xRVXXMTZz5gnVQQZ_lgs/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1hpWA9O5lTdazySQZIbkFiQtq2fxnW3-b/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Z2WzhPWG52acybttNrZQIuG1qsKg_2pA/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QuWgmXWcd2cVbPqZ8bCL7la6QeVzzLrB/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14kLUS2lDdrdDb_lS6nRB-kA3jl93UmBf/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab granets metamorphic Porphyroblastic texture Quartz Inclusions schist https://bereket-haileab.geology.sites.carleton.edu/files/original/0766c6df5ce4927e3c40ac769922a8d1.jpg eb110a94ef3071e22fe70e2fe4e4a3f2 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-111 Subject The topic of the resource Sillimanite Garnet Gneiss Description An account of the resource Major Minerals: garnet, biotite, albite, quartz Minor Minerals: zircon, graphite Optics: pleochroic halo in biotite, pre-kinematic granets Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-111. 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=10815851349f41d182f4d24932b517d0" 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=10815851349f41d182f4d24932b517d0">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gOTDSyswA_cGSP2Q3sHs0pw80udyo5pd/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FOeCkFWyUYEvPHgQGPFlbRxMwKI8m1_i/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1TLGPvuXxRpptriZeYgQ0hfcUs6uYM01f/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Yb9WlvY38u_BSKeazPFltoptg1SZtYxs/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1PAylooRSnUzMjk4G0fM8ZykhMRno2Zwa/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pFM_1R4pmDmAfT4zpP95JqbkErWKSta4/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/109ctqe6-4NuLh8xayHN7Tn9LuAw_z4T2/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OPsgTneZ1OJdbjc_j9VMn7BRBMt8nw-5/preview" allow="autoplay"></iframe> <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fRgLzWOg_feSQgDShsDc6z4IqAHoaOOf/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ljfXUZ0KYazQ6JE0G-rqYEqc6ycOWIAk/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QnUvp9MDxhYoAzvImnLABP7uAM-qP1c_/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab albite twining gneiss metamorphic pleochroic halo in biotite polysynthetic twining pre-kinematic granets https://bereket-haileab.geology.sites.carleton.edu/files/original/b61c13d41b255180cfa802e9739726c8.jpg 41793e209e1a39f9cb247afa3d57d25d 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 BH250-112 Subject The topic of the resource Dish Hill Xenolith Vesicular Olivine Basalt with Vapor-Phase Mineralization Olivine Basalt Showing Degassing Textures and Vapor-Phase Crystal Growth Description An account of the resource <p><strong>Vesicular Olivine Basalt with Vapor-Phase Mineralization and an Olivine-Rich Crystal Aggregate</strong></p> <p><strong>Description</strong></p> <p><strong>Major Minerals:</strong>&nbsp;plagioclase, olivine, volcanic glass</p> <p><strong>Minor Minerals:</strong>&nbsp;clinopyroxene, biotite/phlogopite, Fe-Ti oxides, vapor-phase minerals</p> <p><strong>Textures:</strong>&nbsp;porphyritic, vesicular, pilotaxitic, intergranular, glomeroporphyritic, vapor-phase crystallization, crystal accumulation</p> <p><strong>Overview</strong></p> <p>BH250-112 is an exceptionally instructive volcanic rock that preserves several stages in the evolution of a basaltic magma. The hand sample consists primarily of a dark gray vesicular basalt containing scattered phenocrysts and abundant gas cavities. Near the upper portion of the specimen, a highly vesicular scoriaceous zone records intense volatile exsolution during eruption. Adjacent to this zone is a conspicuous olivine-rich domain (BH250-112C), composed of densely packed green crystals that contrast sharply with the surrounding basalt.</p> <p>Thin section observations reveal a complex history involving magma crystallization, crystal accumulation, degassing, vapor-phase mineral growth, and late-stage alteration. Together, these features make BH250-112 one of the most valuable volcanic teaching specimens in the BH250 Collection.</p> <p><strong>Hand Sample Characteristics</strong></p> <p>The basalt is dark gray to black and contains abundant vesicles ranging from less than one millimeter to several millimeters in diameter. The upper portion of the specimen exhibits a reddish-brown scoriaceous zone characterized by extreme vesicularity, indicating rapid volatile loss during eruption and cooling.</p> <p>The most distinctive feature is the green olivine-rich inclusion exposed near the upper right side of the sample. This crystal-rich zone contains abundant olivine grains and appears texturally distinct from the surrounding basalt. The sharp contact suggests that it may represent an olivine-rich crystal aggregate, cumulate fragment, or crystal-rich enclave entrained within the lava prior to eruption.</p> <p><strong>Petrography of the Host Basalt</strong></p> <p>The basaltic groundmass consists primarily of plagioclase microlites, volcanic glass, minor pyroxene, and opaque oxide minerals. Many areas display a pilotaxitic texture in which plagioclase microlites show weak preferred orientation within a finer matrix, reflecting flow and crystallization during lava emplacement.</p> <p>Larger plagioclase crystals occur as phenocrysts scattered throughout the rock. Under crossed polars, these grains display well-developed albite twinning and low first-order interference colors. Several crystals show fractures and local deformation features, including bent twins and irregular extinction patterns, suggesting mechanical stress during cooling or eruption.</p> <p>Opaque minerals, likely titanomagnetite and related Fe-Ti oxides, occur throughout the groundmass and contribute to the dark color of the rock.</p> <p><strong>Olivine Mineralization</strong></p> <p>Olivine is one of the most important minerals present in BH250-112. Numerous grains exhibit the high birefringence and bright interference colors characteristic of olivine under crossed polarized light. Many crystals are subhedral to anhedral and show irregular fracturing produced during cooling and contraction.</p> <p>The olivine-rich domain is particularly significant. In thin section, this region consists of closely packed olivine crystals forming a crystal-supported texture. Such concentrations commonly develop when early-formed olivine crystals accumulate within a magma chamber or lava conduit before eruption.</p> <p>The texture suggests that the olivine-rich material crystallized prior to final emplacement of the host basalt. Whether this domain represents a crystal accumulation, a cumulate fragment, or a partially disaggregated xenolith cannot be determined with certainty, but its presence demonstrates the physical segregation of early-crystallizing minerals from the surrounding melt.</p> <p><strong>Vesiculation and Degassing</strong></p> <p>The abundance of vesicles throughout the specimen provides direct evidence for volatile-rich basaltic magma. As the magma ascended toward the surface, decreasing pressure caused dissolved gases to exsolve and form bubbles. These bubbles expanded rapidly during eruption, producing the highly vesicular texture observed in both hand sample and thin section.</p> <p>The progression from relatively dense basalt to highly vesicular scoria records increasing gas concentration and decreasing confining pressure. The vesicles preserve a frozen record of magma degassing and provide valuable insight into eruptive processes.</p> <p><strong>Vapor-Phase Crystallization</strong></p> <p>Among the most spectacular features preserved in BH250-112 are the delicate crystal linings developed within many vesicles. Several photomicrographs show radiating sprays of euhedral crystals growing inward from cavity walls. Individual crystals are elongate, prismatic, and commonly arranged in fan-shaped or spherulitic aggregates.</p> <p>These textures are classic examples of vapor-phase crystallization.</p> <p>Following emplacement of the lava, residual magmatic gases circulated through the interconnected vesicle network. These gases carried silica, alkalis, and other volatile components released from the cooling magma. As temperatures declined, minerals precipitated directly onto vesicle walls and grew into open cavities.</p> <p>The resulting textures indicate growth in an open-space environment rather than crystallization from a liquid melt. The minerals responsible for these crystal sprays may include silica polymorphs such as cristobalite or tridymite, alkali feldspar, or zeolitic phases. Definitive identification would require analytical work, but the morphology strongly supports a vapor-phase origin.</p> <p>These features provide outstanding examples of post-eruptive mineral growth and demonstrate how volcanic gases can continue to modify a rock long after primary crystallization has ceased.</p> <p><strong>Mafic Minerals and Late-Stage Magmatic Evolution</strong></p> <p>Several photomicrographs contain brown pleochroic minerals interpreted as biotite or phlogopite. The presence of mica in a basaltic rock suggests that the magma contained elevated concentrations of volatiles, particularly water and potassium-rich components.</p> <p>The occurrence of mica together with abundant olivine and vesicle-filling minerals suggests that BH250-112 may represent an alkaline basaltic magma rather than a strictly tholeiitic basalt. Such magmas commonly contain higher volatile contents and are capable of producing extensive vapor-phase mineralization during cooling.</p> <p><strong>Contact Relationships</strong></p> <p>Thin sections crossing the boundary between the dense basalt and the olivine-rich domain reveal abrupt changes in texture and mineral abundance. The olivine-rich region is markedly coarser and contains a much higher concentration of early-crystallized mafic minerals than the surrounding lava.</p> <p>This relationship suggests that the crystal aggregate formed prior to eruption and was subsequently incorporated into the host magma. Such features provide valuable evidence for crystal sorting and physical processes operating within magma reservoirs.</p> <p><strong>Petrologic Interpretation</strong></p> <p>BH250-112 records a sequence of events that began with crystallization of olivine and plagioclase within a basaltic magma. Some of the early-formed olivine became concentrated into crystal-rich aggregates. As the magma ascended and erupted, dissolved gases exsolved and produced abundant vesicles. Rapid cooling generated the fine-grained pilotaxitic groundmass preserved in the basalt.</p> <p>Following solidification, residual magmatic gases circulated through the vesicle network and deposited spectacular vapor-phase minerals along cavity walls. These late-stage minerals preserve evidence of continued chemical activity within the cooling lava and represent one of the most visually striking features of the specimen.</p> <p><strong>Educational Significance</strong></p> <p>BH250-112 is an outstanding teaching specimen because it preserves numerous volcanic processes within a single rock:</p> <ul> <li>Basaltic mineralogy</li> <li>Olivine crystallization</li> <li>Plagioclase twinning</li> <li>Pilotaxitic texture</li> <li>Crystal accumulation</li> <li>Vesicle formation</li> <li>Magmatic degassing</li> <li>Scoria development</li> <li>Vapor-phase crystallization</li> <li>Late-stage mineral growth</li> <li>Volatile-rich magmatic processes</li> </ul> <p>Students can use this specimen to reconstruct the complete history of a volcanic rock, from crystallization within a magma reservoir to eruption, degassing, cooling, and post-eruptive mineralization. Few samples in teaching collections preserve this range of igneous processes as clearly as BH250-112.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=811406928&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: Dish Hill, California, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-112. 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=5051dc58a5444c9790775764a896862c" 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=5051dc58a5444c9790775764a896862c">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_SDrhqDFDaMW0cJflIPvGyZjNyrv-j9Z/preview" allow="autoplay"></iframe><br /><br />&lt;<iframe width="100%" height="480" src="https://drive.google.com/file/d/1wzIK6tQaV4OfVDfjJMDIx-Qmfdf9sKXf/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-112. <iframe width="100%" height="480" src="https://drive.google.com/file/d/1nHhEP0wi7akaklmv4o5lNTkAX_p_JyO1/preview" allow="autoplay"></iframe> <iframe width="640" height="480" src="https://drive.google.com/file/d/1yfecJ9qOnfeG8Itf-Cv4xxdxDlc2SgmX/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1gjkq_i6RQS0yqoFJ8Sy1b9QOkpnfkIY2/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1zlfGavV5_IMPUTlJUZWWMMJ4JNsL3PkG/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1S_UwDO6VmUzjw7Lodctas6VnC5oAwPlC/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1d3T7cRPO20zNtsA-s5WsCSpyvFBV4nqG/preview" allow="autoplay"></iframe> &lt;iframe width="100%" height="480" src="https://drive.google.com/file/d/1qr9725u4ylZ9hWadIu_Jl7qFc7TNTS8n/preview" <iframe width="100%" height="480" src="https://drive.google.com/file/d/1DMz5d7GBBpbVXOpTDcCMpjRaQKyTsUMJ/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1WGACc-y0l0ZxQIwWmhsrlX7GTQwdEGHY/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab basanite Clinopyroxene Dish Hill Garnet Clinopyroxenite harzburgite Herzolite igneous mantle xenolith Mojave Desert olivine Orthopyroxene plutonic Pyroxenite Spinel Spinel Peridotite ultramafic Wehrlite xenolith https://bereket-haileab.geology.sites.carleton.edu/files/original/673cef037bdcc3324252c20642f40260.jpg b5508688bb56e185a9ff23a00861682e https://bereket-haileab.geology.sites.carleton.edu/files/original/a9a21b5ded1fc1c262e743572b1f293d.jpg 84806158aee11b76da34201c47433b6c 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 BH250-112a Subject The topic of the resource Dish Hill Xenolith Olivine Basalt Host Rock and Xenolith Contact Zone Description An account of the resource <p><strong>BH250-112A</strong></p> <p><strong>Xenolith-Bearing Alkali Basalt with Vapor-Phase Mineralization</strong></p> <p><strong>Dish Hill, Mojave Desert, California</strong></p> <p><strong>Description</strong></p> <p><strong>Major Minerals:</strong>&nbsp;plagioclase, olivine, volcanic glass</p> <p><strong>Minor Minerals:</strong>&nbsp;clinopyroxene, biotite/phlogopite, Fe-Ti oxides, vapor-phase minerals</p> <p><strong>Textures:</strong>&nbsp;porphyritic, vesicular, pilotaxitic, xenolith-bearing, glomeroporphyritic, vapor-phase crystallization</p> <p><strong>Overview</strong></p> <p>BH250-112A is the volcanic host rock that transported the mantle xenolith BH250-112C from the upper mantle to the Earth's surface. Collected from Dish Hill in the eastern Mojave Desert of California, the specimen preserves a remarkable record of volcanic processes ranging from magma crystallization at depth to volatile exsolution, vesicle formation, and late-stage vapor-phase mineral growth. Together with the associated mantle xenolith, the rock provides an exceptional opportunity to study the connection between deep mantle processes and surface volcanism.</p> <p>The hand sample consists of a dark gray to black alkali basalt containing abundant vesicles and a conspicuous green ultramafic xenolith. The sharp contrast between the fine-grained volcanic host and the coarse-grained mantle fragment illustrates the rapid ascent of the magma, which carried pieces of the lithospheric mantle to the surface before they could be completely melted or assimilated.</p> <p><strong>Petrography of the Host Basalt</strong></p> <p>Thin sections reveal a fine-grained basaltic groundmass composed primarily of plagioclase microlites, volcanic glass, pyroxene, and opaque oxide minerals. Many areas display a pilotaxitic texture in which plagioclase laths show a weak preferred orientation produced by magmatic flow prior to solidification. Larger plagioclase phenocrysts are scattered throughout the rock and commonly exhibit well-developed albite twinning under crossed polarized light.</p> <p>Several plagioclase crystals display fractures, bent twins, and irregular extinction patterns that may reflect thermal stress associated with eruption and cooling. Opaque minerals, interpreted as titanomagnetite and related Fe-Ti oxides, occur throughout the groundmass and contribute to the dark color of the rock.</p> <p>Olivine occurs as both isolated phenocrysts and crystal aggregates. Under crossed polarized light the olivine displays bright interference colors, irregular fractures, and locally minor alteration along grain boundaries. The presence of abundant olivine, together with possible phlogopite or biotite observed in several thin sections, suggests that the host magma was relatively rich in volatiles and may be more appropriately classified as an alkaline basalt rather than a typical tholeiitic basalt.</p> <p><strong>Contact with the Mantle Xenolith</strong></p> <p>One of the most important features preserved in BH250-112A is its contact with the associated peridotite xenolith BH250-112C. Thin sections crossing the contact reveal an abrupt transition from fine-grained basalt to coarse-grained mantle peridotite. The basalt wraps around irregular margins of the xenolith and fills embayments along its edges, indicating that the mantle fragment was already solid when it became incorporated into the magma.</p> <p>Localized reaction textures occur near portions of the contact where hot basaltic melt interacted with olivine and pyroxene in the xenolith. Although limited thermal modification occurred during transport, the preservation of coarse mantle textures demonstrates that ascent was rapid. Had the xenolith remained within the magma for a prolonged period, extensive melting and recrystallization would have destroyed much of its original mineralogy.</p> <p>This relationship provides a direct illustration of how basaltic magmas can act as conveyors, transporting fragments of the Earth's mantle from depths of tens of kilometers to the surface.</p> <p><strong>Vesicles and Volcanic Degassing</strong></p> <p>Abundant vesicles are present throughout the basalt and represent one of the most striking features of the specimen. These cavities formed as dissolved volatiles exsolved from the magma during ascent and eruption. As pressure decreased, gas bubbles nucleated and expanded within the melt, producing the vesicular texture now preserved in the rock.</p> <p>The progression from relatively dense basalt to highly vesicular zones records increasing volatile concentration and decreasing confining pressure during eruption. The vesicles therefore provide a direct record of volcanic degassing and preserve evidence of the dynamic processes operating during emplacement of the lava.</p> <p><strong>Vapor-Phase Mineralization</strong></p> <p>Among the most spectacular features preserved in BH250-112A are the crystal-lined vesicles that record the final stages of cooling and chemical evolution within the volcanic system. While most minerals in igneous rocks crystallize directly from a melt, these cavity-filling minerals formed after the lava had largely solidified. The photomicrographs reveal delicate radiating crystal sprays, fan-shaped aggregates, and locally spherulitic growths projecting inward from vesicle walls.</p> <p>As the basalt cooled, volatile components such as H₂O, CO₂, F, Cl, S, Na, K, and Si became increasingly concentrated in residual fluids and gases trapped within the rock. These volatile-rich fluids migrated through the interconnected vesicle network and transported dissolved chemical components through the cooling lava. Minerals subsequently precipitated on vesicle walls and grew into open cavities where they were free to develop euhedral crystal forms.</p> <p>The inward-pointing crystal terminations and radial growth patterns observed in the thin sections are characteristic of vapor-phase crystallization. Such textures indicate unrestricted growth into open space and differ fundamentally from crystals that formed within the melt itself. These minerals represent some of the youngest phases in the rock and record a stage of mineral formation that occurred after primary magmatic crystallization had essentially ceased.</p> <p>Although definitive identification requires analytical techniques such as SEM, X-ray diffraction, or electron microprobe analysis, the crystal morphology and volcanic setting suggest possible: Without SEM, XRD, or microprobe analyses, identification remains tentative, but based on morphology and volcanic setting, likely candidates include:</p> <p><strong>Silica minerals</strong></p> <ul> <li>Cristobalite</li> <li>Tridymite</li> <li>Chalcedony (later)</li> </ul> <p><strong>Alkali feldspars</strong></p> <ul> <li>Sanidine</li> <li>Anorthoclase</li> </ul> <p><strong>Zeolite-group minerals</strong></p> <ul> <li>Phillipsite</li> <li>Chabazite</li> <li>Analcime</li> <li>Natrolite</li> </ul> <p><strong>Late-stage volcanic minerals</strong></p> <ul> <li>Apatite</li> <li>Amphibole microlites</li> <li>Iron oxides</li> </ul> <p>The radiating sprays in your photomicrographs are particularly reminiscent of zeolite and silica vapor-phase growth textures commonly reported from vesicular alkali basalts.</p> <p>The textures are particularly similar to vapor-phase mineral assemblages reported from vesicular alkali basalts worldwide.</p> <p>The abundance of vapor-phase minerals suggests that the Dish Hill magma retained a significant volatile component during cooling and that fluid circulation continued after emplacement. These textures provide compelling evidence that volcanic rocks can remain chemically active long after eruption and offer an excellent opportunity to discuss the transition from primary magmatic crystallization to late-stage fluid-driven mineralization.</p> <p><strong>Petrologic Interpretation</strong></p> <p>BH250-112A records a complex sequence of magmatic and post-magmatic processes. Basaltic magma generated within the mantle ascended toward the surface, entraining fragments of spinel lherzolite from the lithospheric mantle. During eruption, dissolved volatiles exsolved from the magma, producing abundant vesicles throughout the lava. Rapid cooling generated the fine-grained pilotaxitic groundmass, while the mantle xenolith remained largely intact due to rapid ascent.</p> <p>Following solidification, residual magmatic gases and fluids circulated through the vesicle network and precipitated spectacular vapor-phase minerals within open cavities. The resulting rock preserves evidence of magma generation, mantle transport, volcanic degassing, cooling, and late-stage mineralization within a single specimen.</p> <p><strong>Educational Significance</strong></p> <p>BH250-112A is one of the most versatile teaching specimens in the BH250 Collection because it links deep Earth processes with volcanic phenomena visible at the Earth's surface. Students can examine the relationships between mantle xenoliths and their host magma, observe classic volcanic textures, and study vapor-phase mineralization within the same sample.</p> <p>The specimen is particularly valuable for teaching:</p> <ul> <li>Alkali basalt petrology</li> <li>Mantle xenolith transport</li> <li>Basalt–mantle relationships</li> <li>Plagioclase twinning</li> <li>Olivine crystallization</li> <li>Pilotaxitic texture</li> <li>Vesicle formation</li> <li>Volcanic degassing</li> <li>Vapor-phase crystallization</li> <li>Open-space crystal growth</li> <li>Late-stage magmatic fluids</li> <li>Post-eruptive mineralization</li> </ul> <p>Few volcanic specimens preserve such a complete record of igneous processes, making BH250-112A one of the most scientifically informative and visually striking rocks in the BH250 Collection.</p> <br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1695466492&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: Dish Hill, California, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 112a. 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=b3e7bf9f281147b7a95d8e575c7feca1" 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=b3e7bf9f281147b7a95d8e575c7feca1">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wv5AwwywGumlt9VbZd6SOQKmUhPh9Bn_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1zrvKi6WZhXG9BIHpuz2jfThUeHIMJNKl/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Jg2OmRx2GcctvUYTb0-EZPaZEOZPA5si/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1uzXbQa8q_aCUkkTPnClr6_0-sZQw9Sae/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1z-kv6dQUcuVqWogxY6Z-cfItIGWKQOiD/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1tbGh3h-0WC7BeAJFvfDfSukzG6XcoSrw/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1UoG4Wxf1Rx4DIVzxZ-PGHOTkGETcnFpQ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1x4fEUo76wBVDi-74EAb6q_ZlMYP9UwuU/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/13sHUMtWPOG0nuhsmxpGflvcpdtKP104i/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1LX2An8zIdR1gkeFZB9M_Tz7MTnoC6O_1/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10uldNOPXcx6hkE9SUB8EoXE8qV94HTXz/preview" allow="autoplay"></iframe><br />TAS diagram of sample 112a. Creator An entity primarily responsible for making the resource Bereket Haileab Alkali basalt basalt Cima volcanic field Clinopyroxene cristobalite Dish Hill Fan-Shaped Crystal Growth Garnet Clinopyroxenite harzburgite igneous Late-Stage Magmatic Fluids Lherzolite mantle xenolith Mojave Desert olivine Open-Space Filling Orthopyroxene plutonic Post-Magmatic Mineralization Pyroxenite Radiating Crystals scoria Spherulitic Texture Spinel Spinel Peridotite tridymite ultramafic Ultramafic rock Vapor-Phase Crystallization Vapor-Phase Minerals Vesicle-Lining Crystals vesicular basalt Volcanic Degassing Volcanic Gas Alteration Wehrlite xenolith Zeolites https://bereket-haileab.geology.sites.carleton.edu/files/original/2ee54b29cf9493349b90788f11275b33.jpg 8c9fa4cfe3c29ce43016589064d0961d https://bereket-haileab.geology.sites.carleton.edu/files/original/4cc02d9a5cb9bdadb16d840026a55931.jpg ea66f76e10ec7697cbe715380e137efc 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 BH250-112c Subject The topic of the resource Spinel Lherzolite Mantle Xenolith, Dish Hill, California Description An account of the resource Major Minerals: olivine, orthopyroxene, clinopyroxene Minor Minerals: spinel, Fe-Ti oxides, minor serpentine alteration Textures: granular, protogranular, xenolithic, mantle-derived Overview BH250-112C is a mantle-derived xenolith enclosed within an alkali basalt erupted at Dish Hill, California. The specimen represents a rare fragment of the upper mantle that was transported rapidly to the Earth's surface by ascending basaltic magma. Mantle xenoliths such as this provide some of the most direct evidence available for the composition, texture, and evolution of the lithospheric mantle beneath western North America. In hand sample, the xenolith appears as a greenish crystal-rich inclusion sharply enclosed within the darker volcanic host rock. Thin sections reveal a coarse-grained assemblage dominated by olivine and pyroxene that contrasts strongly with the fine-grained basaltic matrix. The mineral assemblage and texture are most consistent with a spinel lherzolite, the most common rock type of the shallow upper mantle. Geological Setting Dish Hill is a Quaternary cinder cone located within the eastern Mojave Desert near Ludlow, California. The volcanic center is well known for its abundant mantle xenoliths, which were entrained by rapidly ascending alkali basalt magmas. These eruptions sampled the subcontinental lithospheric mantle and delivered fragments of deep mantle rocks to the surface with minimal modification. The Dish Hill xenolith suite has been extensively studied because it provides a window into the composition, deformation history, and metasomatic evolution of the mantle beneath the Mojave Desert. BH250-112C represents one of these mantle samples and offers a direct connection between deep Earth processes and surface volcanism. Mineralogy The xenolith is composed primarily of olivine accompanied by both orthopyroxene and clinopyroxene. This assemblage is characteristic of lherzolite, a fertile mantle rock capable of producing basaltic magmas through partial melting. Olivine is the dominant mineral phase and forms large anhedral to subhedral grains throughout the specimen. Orthopyroxene occurs as low-birefringence grains intergrown with olivine, whereas clinopyroxene exhibits slightly higher birefringence and occupies interstitial positions between larger crystals. Small opaque grains are interpreted as spinel-group minerals and occur along grain boundaries and triple junctions. The coexistence of olivine, orthopyroxene, clinopyroxene, and spinel distinguishes the xenolith from dunite and harzburgite and strongly supports classification as a spinel lherzolite. Petrography The thin sections display a coarse-grained granular texture typical of upper mantle peridotites. Individual mineral grains commonly range from several hundred micrometers to more than a millimeter in diameter and form an interlocking mosaic of olivine and pyroxene. Olivine exhibits bright second-order interference colors, irregular fracturing, and locally undulose extinction. These features record deformation and recrystallization under mantle conditions prior to eruption. Orthopyroxene is recognized by its relatively subdued interference colors and lower birefringence, whereas clinopyroxene displays slightly brighter interference colors and more complex extinction behavior. Many grain junctions approach 120°, indicating prolonged textural equilibration and recrystallization at high temperatures. Such equilibrium textures are characteristic of mantle rocks that have resided at depth for extended periods. Small opaque grains interpreted as spinel occur between silicate grains and further support a spinel-facies mantle origin. Evidence for a Mantle Origin Several petrographic characteristics indicate that BH250-112C originated within the upper mantle: • Dominance of olivine and pyroxene. • Presence of both orthopyroxene and clinopyroxene. • Granular equilibrium texture. • Triple-junction grain boundaries. • Absence of volcanic groundmass. • Sharp contact with the enclosing basalt. • Presence of spinel consistent with upper mantle pressures. These features differ fundamentally from those of igneous cumulates or crystal accumulations formed within shallow magma chambers. Instead, they reflect the slow cooling, deformation, and recrystallization expected within the lithospheric mantle. Interaction with the Host Basalt Although the xenolith remains remarkably well preserved, its margins record limited interaction with the surrounding basaltic magma. Minor fracturing, localized alteration, and subtle modification of grain boundaries likely developed during transport to the surface. The preservation of the original mantle texture indicates rapid ascent. Had the xenolith remained within the magma for a prolonged period, extensive melting and recrystallization would have destroyed much of its primary mineralogy and texture. Instead, the basalt acted as a conveyor, transporting the xenolith from mantle depths to the surface while preserving much of its original character. Interpretation Based on its mineral assemblage and texture, BH250-112C is interpreted as a spinel lherzolite mantle xenolith derived from the subcontinental lithospheric mantle beneath the Mojave Desert. Spinel lherzolite is considered a relatively fertile mantle composition and is widely regarded as an important source rock for basaltic magmas. The xenolith therefore provides a direct sample of the mantle reservoir from which many volcanic rocks ultimately originate. The coarse-grained equilibrium texture, the presence of both pyroxenes, and the occurrence of spinel collectively indicate formation under upper mantle conditions. Subsequent entrainment by alkali basalt magma transported the xenolith rapidly to the surface, preserving a rare record of mantle mineralogy, deformation, and thermal history. Geological and Educational Significance Peridotite xenoliths provide a unique opportunity to examine rocks that normally reside tens of kilometers beneath the Earth's surface. BH250-112C allows students to study the mineralogy of the upper mantle directly and serves as an excellent introduction to mantle petrology and basalt genesis. The specimen is particularly valuable for teaching: • Mantle composition and structure • Peridotite classification • Olivine and pyroxene identification • Spinel-facies mantle mineralogy • Partial melting and basalt generation • Xenolith transport mechanisms • Mantle deformation and recrystallization • Relationships between mantle rocks and volcanic magmas Few teaching specimens provide such a direct connection between deep Earth processes and volcanic activity. BH250-112C is therefore one of the most important mantle petrology samples in the BH250 Collection. Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 112c. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <br /><iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=4d517a7cf95a4fee80445991a6d9b042" 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=4d517a7cf95a4fee80445991a6d9b042">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/162_Oe1zrI96csK22etBwDkSMk6lQWVLn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1rTTfKv4FtrRt3eR0Y9DpYLTtaVtKWBpe/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1J8d_C6pTNzvVy9GSmGGMYYUeJWUORuIG/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1XhnLcngQy5rS4LTGYIgvsmKgZF_O0FLN/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wRhB53t5Mf66Qh7L-3_i0eQTMGVNFA59/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FMvhVejbJ-CTE9i-gKIOio5qtChAGXyj/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1c9JmNbqZYGD8wI90PUAfKk3PGCaRgX33/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10qwAfWfg6JelCUZ4WQMorg8ZjKyyE1EL/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1SHx--P5RyGXRzQBvZqHNl2Z-z82ly9sK/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1S_UwDO6VmUzjw7Lodctas6VnC5oAwPlC/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1LX2An8zIdR1gkeFZB9M_Tz7MTnoC6O_1/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Alkali basalt Cima volcanic field Clinopyroxene Dish Hill Garnet Harzburigte igneous Lherzolite Lithospheric Mantle Mantle Petrology mantle xenolith Mojave Desert olivine Orthopyroxene Partial melting peridotite plutonic Spinel Spinel Lherzolite Spinel Peridotite ultramafic Ultramafic rock upper mantle xenolith https://bereket-haileab.geology.sites.carleton.edu/files/original/b80e699b605ccff60f2700f765202db1.jpg 7fa3318725df22e5fd4a6eff8d26b733 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 BH250-113 Subject The topic of the resource Duluth Gabbro Description An account of the resource Major Minerals: plagioclase, clinopyroxene, orthopyroxene <br />Minor Minerals: biotite, oxides<br /> <p><strong>BH250-113 — Duluth Gabbro</strong></p> <p data-start="285" data-end="1060">BH250-113 is another excellent specimen from the Duluth Complex of northeastern Minnesota, one of the most famous layered mafic intrusions in North America and an important component of the<span>&nbsp;</span><strong data-start="475" data-end="524">1.1-billion-year-old Midcontinent Rift System</strong>. Like other rocks from the Duluth Complex, this sample records the crystallization of large volumes of mafic magma that ponded within the crust and slowly cooled to produce coarse-grained intrusive rocks dominated by plagioclase and pyroxene. While BH250-50 emphasizes classic fresh gabbroic mineralogy and cumulate textures, BH250-113 offers a different and equally valuable teaching opportunity because it demonstrates how weathering can significantly alter the visual appearance of igneous rocks and complicate field identification.</p> <p data-start="1062" data-end="2038">At first glance, the hand sample presents two very different appearances depending on which surface is examined. The weathered surface displays a light tan to beige coloration where alteration products partially obscure the original mineralogy. Dark minerals appear as scattered brown to black patches, and the rock may initially look more felsic or altered than it truly is. However, freshly broken surfaces reveal the rock’s true identity: a dark, coarse-grained mafic intrusive rock composed of interlocking crystals of<span>&nbsp;</span><strong data-start="1585" data-end="1634">plagioclase, clinopyroxene, and orthopyroxene</strong>, with minor oxides and biotite. This contrast makes BH250-113 an outstanding specimen for teaching students one of the most important lessons in field geology: always examine a fresh surface before identifying an igneous rock. Weathered surfaces can be deceptive, especially in mafic rocks where feldspars alter to clay minerals and ferromagnesian minerals oxidize or break down into secondary products.</p> <p data-start="2040" data-end="2818"><strong data-start="2040" data-end="2145">BH250-127 provides an excellent comparison because it demonstrates the opposite effect of weathering.</strong><span>&nbsp;</span>In this carbonate-rich sedimentary rock, weathered surfaces actually enhance geological interpretation by exposing subtle bedding, stylolitic seams, dissolution features, and internal sedimentary fabrics that are less obvious on freshly broken surfaces. Weathering preferentially removes softer carbonate material and accentuates textural contrasts, making depositional and diagenetic features easier to observe. When students compare BH250-113 and BH250-127 side by side, they quickly learn an important geological principle: in many igneous rocks, fresh surfaces reveal the most useful information, whereas in carbonate rocks, weathered surfaces may tell a richer story.</p> <p data-start="2820" data-end="3512">Under the microscope, BH250-113 reveals classic<span>&nbsp;</span><strong data-start="2868" data-end="2902">ophitic to subophitic textures</strong>, where elongate plagioclase laths are partially enclosed by larger pyroxene crystals. These textures indicate crystallization in a slowly cooling magma chamber where plagioclase formed early and pyroxenes crystallized later around them. Some areas display more equigranular interlocking textures, while others show localized<span>&nbsp;</span><strong data-start="3228" data-end="3256">poikilitic relationships</strong>, where larger pyroxene crystals enclose smaller mineral grains. These textural variations reflect changing crystallization conditions within the magma chamber and demonstrate that even within a single hand sample, magmatic textures can be highly variable.</p> <p data-start="3514" data-end="4111">The photomicrographs also show evidence of late-stage magmatic evolution and post-crystallization alteration. Biotite occurs in minor amounts and likely formed during later stages of crystallization as water and incompatible elements became concentrated in the remaining melt. Oxide minerals occur as opaque grains distributed throughout the rock and may represent magnetite or ilmenite. Some altered zones display secondary minerals that formed during weathering or hydrothermal alteration, further emphasizing that this rock records both primary igneous processes and later surface modification.</p> <p>The photomicrographs of<span>&nbsp;</span><strong data-start="1212" data-end="1241">BH250-113c and BH250-113d</strong><span>&nbsp;reveal unusual vermicular intergrowth textures that resemble classic myrmekite, but with an important difference. Traditional myrmekitic textures typically consist of worm-like quartz intergrowths within plagioclase adjacent to potassium feldspar and are most commonly observed in granitic or metamorphic rocks. In this sample, however, the vermicular texture appears to be associated with&nbsp;</span><strong data-start="1632" data-end="1674">iron oxide minerals rather than quartz</strong>, suggesting a different origin. These oxide-rich intergrowths may reflect late-stage magmatic oxidation, exsolution of Fe-Ti oxides from pyroxene, or secondary replacement processes during subsolidus cooling and hydrothermal alteration. Their occurrence highlights the complex post-crystallization history of the Duluth Gabbro and reminds students that similar-looking textures may form through very different geological processes depending on mineral composition and tectonic setting.</p> <p data-start="4113" data-end="4884">Geochemically, BH250-113 is consistent with the broader Duluth Complex and falls within the mafic range, characterized by elevated<span>&nbsp;</span><strong data-start="4244" data-end="4266">Fe, Mg, Ca, and Ti</strong><span>&nbsp;</span>and relatively low silica and alkali contents. These chemical characteristics reflect derivation from mantle-derived basaltic magmas associated with continental rifting. In parts of the Duluth Complex, early-formed cumulate layers are enriched in chromium and nickel, reflecting early crystallization of olivine and pyroxene. More evolved portions may show enrichment in incompatible trace elements and subtle rare earth element fractionation. These geochemical patterns provide evidence for fractional crystallization, magma recharge, and complex open-system magmatic evolution within the large Duluth magma chamber.</p> <p data-start="4886" data-end="5405">Geochemically, BH250-113 is consistent with the broader Duluth Complex and falls within the mafic range, characterized by elevated<span>&nbsp;</span><strong data-start="498" data-end="520">Fe, Mg, Ca, and Ti</strong><span>&nbsp;</span>and relatively low silica and alkali contents, reflecting derivation from mantle-derived basaltic magmas associated with continental rifting during formation of the Midcontinent Rift System. High concentrations of chromium and nickel in some portions of the Duluth Complex reflect early crystallization and accumulation of olivine and pyroxene in basal cumulate layers, whereas more evolved portions tend to show enrichment in incompatible elements such as Ti, P, Zr, and rare earth elements.</p> <p data-start="1017" data-end="1973">Rare Earth Element (REE) patterns from the Duluth Complex commonly show<span>&nbsp;</span><strong data-start="1089" data-end="1149">moderate enrichment in light rare earth elements (LREEs)</strong><span>&nbsp;</span>relative to heavy rare earth elements (HREEs), suggesting fractional crystallization and progressive evolution of the magma. Some samples also display subtle to moderate<span>&nbsp;</span><strong data-start="1320" data-end="1356">negative europium (Eu) anomalies</strong>, which reflect the removal of plagioclase during crystallization because europium can substitute into calcium-rich feldspar. In contrast, samples with abundant accumulated plagioclase may show weak positive Eu anomalies. These REE patterns provide important evidence that the Duluth magma chamber was not chemically static—it evolved through repeated crystal settling, magma recharge, and localized chemical differentiation. BH250-113 helps students connect what they observe in hand sample and thin section with larger geochemical processes operating within one of North America’s most important layered intrusions.</p> <p>The Duluth Complex remains globally significant not only because of its impressive size and layered structure, but also because it helps geologists understand magma chamber processes, continental rifting, and economically important<span>&nbsp;</span><strong data-start="5118" data-end="5146">Ni-Cu-PGE mineralization</strong>. BH250-113 contributes to that story while also serving as a powerful teaching specimen that reminds students that rocks do not always reveal their secrets easily. Sometimes the most important first step in geology is simply knowing which surface to trust.</p> <br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=505668964&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, Minnesota, USA Date A point or period of time associated with an event in the lifecycle of the resource Summer 2012 Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 113. 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=7e6c29529ad241fa9eda1cf084a6538c" 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=7e6c29529ad241fa9eda1cf084a6538c">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/11AIjNVst40iuOphjLJP4YJskGBAgIPt-/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OIF1E2BoBhQNsQ0KWxVmDQB3Cjy8K9dR/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IkJtHfmxBwKmxmm582LCS6S3e0RLh5Wt/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1jQAqAfJpB9AmEGa6cuSwiqRswP6lOh50/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/15nWqEG4V7envO8dn7XbG-3oka8beAbpb/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1GqbK64zM0_dw4k1CkTAU5jZv5NDWCmUn/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1CiiDDbQy8NWcdXeFX77DR9gwrDBi9CXo/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Ef5irMurGqu-qovpcCIw_duVmdDr2RV0/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-XKDUb2yTxlDAK3VbNGVLTx3lCEu7nST/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wY40_C9lpQoQPkfyZgGUzEGCAZMs9XxT/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1rbQnto1Vba9uRFUSlWiH2uO2XugL51QZ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Llmdo9S_4Bip7sOfDH5Q_eHSh3ndPBKa/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-113. Creator An entity primarily responsible for making the resource Bereket Haileab Adcumulates altered surface Anorthite Augite Biotite Bronzite carbonate weathering comparison chemical weathering chromium Clinopyroxene continental rifting Crystal Settling Cumulate texture cumulate textures Duluth Complex Duluth Gabbro europium anomaly Fe-Mg rich rocks Fe-Ti oxides Fractional crystallization fresh surface fresh vs weathered rock surfaces gabbro Hydrothermal alteration Hypersthene igneous Ilmenite interlocking texture iron oxide intergrowth late-stage oxidation Layered intrusion Layered mafic intrusion Layered Texture LREE enrichment mafic Mafic Composition mafic geochemistry Mafic intrusion Mafic Intrusive Rock magma chamber processes magma recharge Magmatic Differentiation Magnetite Mesocumulates Mesoproterozoic microscopic textures Midcontinent Rift Minnesota geology myrmekite-like texture myrmekitic texture Ni-Cu-PGE mineralization nickel ophitic texture Orthopyroxene oxidation oxide exsolution texture oxide intergrowth Oxide minerals petrographic textures Plagioclase plutonic plutonic rocks poikilitic texture Proterozoic Geology Pyroxene alteration rare earth elements reaction textures REE patterns replacement texture rhythmic layering secondary mineralization Sedimentary Structures stylolites Subophitic texture subsolidus alteration Surface Alteration trace elements Ultramafic Rocks unweathered surface vermicular intergrowth vermicular texture weathered surface Weathering Weathering Effects weathering rind https://bereket-haileab.geology.sites.carleton.edu/files/original/92877552422ba7aed4858acf41015fdf.jpg a27ffe18a73f4ffbf4061bf5ddbfa6d0 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 BH250-114 Subject The topic of the resource Basaltic andesite Description An account of the resource Major Minerals: plagioclase, clinopyroxene, orthopyroxene <br />Minor Mineral: chlorite <br /><br /> <p>BH250-114 chemically plots in the basaltic andesite field on a TAS (Total Alkali-Silica) diagram. Basaltic andesite is an intermediate volcanic rock that bridges the compositional gap between basalt and andesite. It plays a significant role in igneous petrology, particularly in subduction-related volcanic arcs.</p> <p>This rock type is characterized by an intermediate silica content, typically ranging from 52–57 wt% SiO₂—richer in silica than basalt, but less than true andesite. Other key chemical features include moderate alkali levels and variable magnesium and iron contents, reflecting processes like fractional crystallization and magma mixing.</p> <p>Sample BH250-114 exhibits a fine-grained (aphanitic) texture, consistent with rapid cooling at or near the Earth’s surface. This texture, along with its chemistry, supports its classification as a basaltic andesite and highlights its origin from a volcanic arc tectonic setting.</p> <br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1792415072&amp;single=true&amp;widget=true&amp;headers=false"></iframe> Date A point or period of time associated with an event in the lifecycle of the resource Summer 2012 Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 114. 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=100931ef44d74999bf60a14e9bdbb05e" 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=100931ef44d74999bf60a14e9bdbb05e">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FhD3RMjs29JNXhHEf7RNn_dbgnJDMfnG/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/11t0oSIRO81qw2XmtfeBLZRYHHdc5rmhe/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1nF1lENixwXl6I9D7zyekj7v6mNBnBQaU/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1r99hscj6jB01xomlssaubKYDkEvWxYBA/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-114. Creator An entity primarily responsible for making the resource Bereket Haileab andesite Aphanitic Texture basalt Basaltic Andesite igneous Intermediate composition mafic volcanic Volcanic rock https://bereket-haileab.geology.sites.carleton.edu/files/original/3d857cfcb575111e7bb737741dee2bb4.jpg a726d9dd6b921a4f3e541e68ff661dee 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-115 Subject The topic of the resource Gneiss Description An account of the resource Major Minerals: quartz, biotite Minor Minerals: plagioclase, hematite Mineralogy Comments: biotite alteration BH250-115 – Gneiss from Glacial Material near Northfield This specimen is a gneiss collected from glacially transported material near Northfield. It displays a well-developed gneissose metamorphic fabric, characterized by distinct mineral banding and alignment of platy and elongate minerals. The texture reflects high-grade regional metamorphism, likely originating from deep crustal rocks before being incorporated into glacial deposits and transported to its present location. 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: Northfield, Minnesota, USA Found in the Carleton Rock Garden Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 115. 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=d0d920aa7f2f491194c40e5ec787b60a" 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=d0d920aa7f2f491194c40e5ec787b60a">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14exEG-tbf1H2aTKSMpmhwkVeRmLfw6Eu/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dbE0d-PTEkWxEvMN1oyQ8zpvUbcoTdY1/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1H8UnZQZUQ_DQRMkLMFJYU6KDEa0oa2L6/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1CVT1XhaKR52-rAvPlpMlTQTC-adIyBEC/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1_D1i774Y9Ss-PeXOelOjZPBTxP_aEqEx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1UWpfOIocYI77dalRGefwbK5CU3WUb7yg/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bWPkKJe8v2k6S6kWEdWqHkSYbmdVY0wK/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab gneiss metamorphic https://bereket-haileab.geology.sites.carleton.edu/files/original/0786e111d16117a6ab481111dfe5b0f8.jpg 9f0ac6ab0f0b0852fcd3a8bf08b0a0e6 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 BH250-116 Subject The topic of the resource Rhyolite 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: Northern Minnesota, Minnesota, USA Found near Split Rock Lighthouse Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 116. 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/18iHhGFtZU0APqRl9mXZi8_XliCWiR3S2/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Description An account of the resource BH250-116 – Rhyolite from Lighthouse Point, North Shore Area This specimen is a rhyolite collected from Lighthouse Point along Minnesota’s North Shore. The rock preserves vesicular textures formed by trapped volcanic gases during solidification. These vesicles are now filled with secondary minerals, likely including quartz, calcite, or zeolites, deposited from hydrothermal fluids or low-temperature alteration after emplacement. The fine-grained groundmass and silica-rich composition reflect its origin from high-viscosity felsic lava, characteristic of explosive volcanic environments. felsic igneous rhyolite volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/c1958a54d41cd0e9d78334bb2e5f2f83.jpg 605a62a16f0237620c2301b8c0839a90 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-117 Subject The topic of the resource Schist Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Northfield, Minnesota, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 117. 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="480" src="https://drive.google.com/file/d/1xwky2v9SpMYOikDtOB20W3QdX-K8fyO_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10q-1Yz6JjFGVMGuWpBLka9Og0Ri2mmKd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Y0BwAGZFJvyRq8m5LtKapRpc3ZdM-u3E/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1cKcNOsLLkwwtjWvck2A4jaD6yHDeIf4a/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1wPtFdbd55FmKLVPeF-irWjJFwigpXFTm/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bsYL2hOqTlNhMIa-hwMafQcyma8z21Sd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" iframe="" src="https://drive.google.com/file/d/1V3Z2SO2n6R_vZK9AJKDy-hQoehVmKORO/preview" allow="autoplay"></iframe> src="https://drive.google.com/file/d/1DoY7hRpSSIU2UnjAA1Hbno-dWO4CWnUq/preview" allow="autoplay"&gt;&nbsp;<br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1FQvSlOoOoQVqK8Y-lkLu718FsAII-5GT/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Description An account of the resource BH250-117 – Muscovite–Quartz Schist with Boudinage Structures This specimen is a muscovite–quartz schist in which the quartz crystals are strongly deformed, exhibiting classic boudin-type structures formed by extension and layer-parallel stretching. In thin section, the schistosity is defined by the parallel alignment of muscovite flakes, some of which are preserved as inclusions within the quartz crystals. These internal mica trails record the rock’s progressive deformation history, where earlier fabric was overprinted by later quartz recrystallization and stretching. The texture reflects intense ductile deformation under regional metamorphic conditions. Boudinage Deformed Quartz metamorphic schist Schist Muscovite schist Muscovite Schistose https://bereket-haileab.geology.sites.carleton.edu/files/original/369f63a256401eea96ffd8c241786f91.jpg 863af2101ae1c7794f374f6833ca7069 https://bereket-haileab.geology.sites.carleton.edu/files/original/fe4e10d7b2f5969cbd7f3e9cfe1bbe5b.jpg a4ab6f7295a813c9ce3e84593676a289 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-118 Subject The topic of the resource Morton Gneiss Description An account of the resource Major Minerals: orthoclase, microcline, quartz, hornblende, chlorite, sericite<br /><br /> <p>BH250-118, BH250-118b, and BH250-118c are samples collected from the Morton Gneiss in Morton, Minnesota. The Morton Gneiss is one of the oldest known rocks in North America and is a widely studied example of high-grade metamorphic rock. It is prominently exposed in southwestern Minnesota, particularly around the town of Morton, from which it takes its name. Here, active quarries reveal striking outcrops of the gneiss, displaying its distinctive banding. Historically, the rock was quarried for use in tabletops, building walls, and tombstones, and quarrying continues today under the ownership of a company based near St. Cloud. The site has also been of academic interest, with recent Carleton College graduate Emma Watson (Class of 2023) completing her comprehensive thesis on the Morton Gneiss.</p> <p>The Morton Gneiss is Archean in origin, with its protolith (original rock) forming around 3.6 billion years ago. Since its formation, it has undergone multiple episodes of metamorphism and deformation, most notably during the Penokean orogeny (~1.85 billion years ago) and later thermal/metamorphic overprinting during the Proterozoic. It is a banded, migmatitic gneiss, showing evidence of both solid-state metamorphism and partial melting (migmatization). The rock features interlayered felsic bands (BH250-118), mafic bands (BH250-118b), and amphibolite (BH250-118c), each representing different compositions, origins, and metamorphic histories.</p> <p>The felsic portion (BH250-118) is light pink to gray in color and composed mainly of quartz, K-feldspar (orthoclase and microcline), plagioclase, and biotite, with minor zircon. It is coarse-grained and foliated, often displaying leucosome veins that formed from partial melting. Its origin is thought to be granitic or granodioritic protoliths that underwent high-grade metamorphism and partial melting. In contrast, the mafic portion (BH250-118b) forms dark gray to black bands and is composed of hornblende, biotite, and more calcic plagioclase. These bands are finer-grained and more resistant to weathering than the felsic layers and are interpreted as amphibolitized mafic intrusions or original mafic layers within the crust that were metamorphosed alongside the felsic material.</p> <p>BH250-118b is the mafic part of the Morton Gneiss which is characterized by dark gray to black bands. Its mineralogy includes hornblende, biotite, and more calcic plagioclase, and it is finer-grained and generally more resistant to weathering than the felsic layers. This mafic material is interpreted as amphibolitized mafic intrusions or original mafic crustal layers that were metamorphosed contemporaneously with the felsic components.</p> <p>Amphibolite (BH250-118c) is present as lenses or layers within the Morton Gneiss and represents metamorphosed mafic rocks that may have originated as basaltic or gabbroic intrusions, or as volcanic sediments. Amphibolite in this setting is dominated by hornblende and plagioclase, typically lacking quartz. It can occur conformably with the gneissic layering or as discordant bodies, suggesting emplacement as dikes during or before metamorphism.</p> <p>Geologically, the Morton Gneiss is significant because it preserves a record of early Earth crustal evolution, including crust formation, tectonism, and high-grade metamorphism. It forms part of the Minnesota River Valley subprovince, which is itself a key component of the Superior Province of the Canadian Shield. Interestingly, in the past, outcrops of the Morton Gneiss were considered as potential storage sites for radioactive waste, and remnants of that period—including test wells and excavated pits—can still be seen in certain locations.</p> <p>The Morton Gneiss is highly weathered in places, and a saprolite has developed on it at several sites near Redwood Falls and Granite Falls, Minnesota. Saprolite samples BH250-100, 100b, 100c, and 100d were collected from these locations. Several student projects have investigated this topic—please refer to the papers, abstracts, and posters available on the Geochemistry of Natural Waters website for more information.</p> <p><br />There are large samples that we brought from Moton in the rock garden.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1170354995&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: Morton, Minnesota, USA GPS Coordinates: 44°33'7.12"N, 94°59'29.41"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-118. 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=af55da0d4a4c485ea324116feab92440" 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=af55da0d4a4c485ea324116feab92440">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14TQeOnCm06omPernZ9dR-QHVlnYOdnjb/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Xj92dBa9AOVMyFUUwN7pAtM5RHTKqf2D/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QrmpDnLHejo9V51ULXD0XNI-1YrcD9Q_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1SIHr0_IZhOMNQBT_GFC1bVpxJkQaT508/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19AIvltxVz9NKzRTKPWAJJZBBHhNT0iS_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JLXYLYkY6JERKRZHe6GIBFvOkqSFAZCX/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1U5ets6zsvvNbK4-Ix5Oq7-SjWXZ1FKxV/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1wP1dBGW3zLn2i409RlmanQMfl-qgRR2-/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1FHy8p7Y2S3QIDGfPCQgYlTy5LjvO-3tX/preview" allow="autoplay"></iframe>&gt;<iframe width="100%" height="480" src="https://drive.google.com/file/d/1bD4xkklyf0aZQyNIcuEKp41_RLVsJtyd/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab amphibolite Amphibolitized Intrusion Archean Gneiss Banded Gneiss Canadian Shield Felsic Gneiss gneiss Granitic Protolith High-Grade Metamorphic Rock Leucosome Veins Mafic Gneiss metamorphic Metamorphosed Mafic Rock Migmatitic Gneiss Minnesota Minnesota River Valley Subprovince Morton Morton Gneiss Partial Melting Features Penokean Orogeny Proterozoic Overprinting Quartz-K-feldspar-Plagioclase-Biotite Radioactive Waste Test Site saprolite https://bereket-haileab.geology.sites.carleton.edu/files/original/ff5a4776db36b63f0038a7c278b1a5b0.jpg 3d8cb734e4e345d486992c1d8ee360a7 https://bereket-haileab.geology.sites.carleton.edu/files/original/29f1af1e8ef0ba1f46cd792fcab6b7e1.jpg 689891746789a32f73caab4a3635967e 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-118b Subject The topic of the resource Tonalite Description An account of the resource Major Minerals: amphiboles, biotite, quartz, plagioclase Minor Minerals: sericite, chlorite, apatite, zircon BH250-118, 118b, and 118c are samples collected from the Morton Gneiss near Morton, Minnesota. The Morton Gneiss is one of the oldest known rocks in North America and a classic example of high-grade metamorphic crust. It is prominently exposed in southwestern Minnesota, especially around the town of Morton, where active and historic quarries reveal spectacular banded outcrops. These exposures have been quarried in the past for use as tabletops, building veneers, and tombstones, and the resource is still being worked today by a company near St. Cloud, Minnesota. The Morton Gneiss is Archean in origin, with its protolith forming around 3.6 billion years ago. Since its formation, the rock has undergone multiple episodes of metamorphism and deformation, most notably during the Penokean Orogeny (~1.85 Ga), followed by additional thermal and metamorphic overprints during the Proterozoic. Recent work, including the comprehensive thesis research by Carleton graduate Emma Watson (Class of 2023), has helped clarify the complex history recorded in these rocks. Texturally and compositionally, the Morton Gneiss is typically described as a migmatitic, banded gneiss, exhibiting both evidence of high-grade solid-state metamorphism and partial melting (migmatization). BH250-118 represents the felsic portion: light pink to gray in color, coarse-grained and foliated, and dominated by quartz, K-feldspar (orthoclase and microcline), plagioclase, and biotite, with minor zircon. It frequently displays leucosome veins, indicating partial melting, and is interpreted to derive from granitic to granodioritic protoliths that were strongly reworked during high-grade metamorphism. BH250-118b is the mafic part of the Morton Gneiss, characterized by dark gray to black bands. Its mineralogy includes hornblende, biotite, and more calcic plagioclase, and it is finer-grained and generally more resistant to weathering than the felsic layers. This mafic material is interpreted as amphibolitized mafic intrusions or original mafic crustal layers that were metamorphosed contemporaneously with the felsic components. BH250-118c is an amphibolite lens or layer within the gneiss, representing metamorphosed mafic rock—either originally intruded as basaltic/gabbroic material or deposited as volcanic protoliths. Its composition is dominated by hornblende and plagioclase and often lacks quartz. These amphibolites may occur conformably with the gneissic fabric or as discordant bodies, possibly reflecting late-stage dike intrusions during or prior to metamorphism. Geologically, the Morton Gneiss records early Earth crustal evolution, including formation, deformation, partial melting, and high-grade metamorphism. It is part of the Minnesota River Valley subprovince, itself a component of the Superior Province of the Canadian Shield. At one time, some outcrops of Morton Gneiss were evaluated for use in radioactive waste storage; remnants of test wells and exploratory quarrying for that purpose can still be observed in certain locations. 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: Morton, Minnesota, USA GPS Coordinates: 44.5532, -94.992694 Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-118b. 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="480" src="https://drive.google.com/file/d/1UT4B5QiMaynsIRuaycsoSi00awse6Uha/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1pgSBqT_V0F5L33AhK3pdhag709fZ-IoD/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1gCscFqGcI_qja2uiOsim0iPb8ZdUyC5T/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/10PUyCy50XiExccTRDtlOQVHW_gX1QsD0/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1SOyU3Ut766mPsU2zSCmQTe1rzX43bXCq/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZqxYH0IMfaQAWPGWTYncpeILzZ7ur_QF/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ejCVtVJOQ9h7owQwoW5N9rnpZX5wijoS/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1w9LkL73s8eeIuCt9l3u4No0NmNAT2hZV/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1U5ets6zsvvNbK4-Ix5Oq7-SjWXZ1FKxV/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1wP1dBGW3zLn2i409RlmanQMfl-qgRR2-/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1FHy8p7Y2S3QIDGfPCQgYlTy5LjvO-3tX/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bD4xkklyf0aZQyNIcuEKp41_RLVsJtyd/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab amphibolite Amphibolitized Intrusion Archean Gneiss Banded Gneiss Canadian Shield Felsic Gneiss gneiss Granitic Protolith High-Grade Metamorphic Rock Leucosome Veins Mafic Gneiss metamorphic Metamorphosed Mafic Rock Migmatite Migmatitic Gneiss Minnesota Minnesota River Valley Subprovince Morton Morton Gneiss Partial Melting Features Penokean Orogeny Proterozoic Overprinting Quartz-K-feldspar-Plagioclase-Biotite Radioactive Waste Test Site Stromatic Migmatite https://bereket-haileab.geology.sites.carleton.edu/files/original/a4fa0637f553bf0b8a4dcf4e75e386e0.jpg 4541fd6593b966cb160663b09d03541e https://bereket-haileab.geology.sites.carleton.edu/files/original/e59151e8502db747658a3dd2bb97d8c5.jpg 8c69d2e4c418e23054e53a40d10bcb55 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-118c Subject The topic of the resource Amphibolite Description An account of the resource Major Minerals: amphibole, biotite, orthoclase BH250-118, BH250-118b, and BH250-118c are samples collected from the Morton Gneiss in Morton, Minnesota. The Morton Gneiss is one of the oldest known rocks in North America and is a widely studied example of high-grade metamorphic rock. It is prominently exposed in southwestern Minnesota, particularly around the town of Morton, from which it takes its name. Here, active quarries reveal striking outcrops of the gneiss, displaying its distinctive banding. Historically, the rock was quarried for use in tabletops, building walls, and tombstones, and quarrying continues today under the ownership of a company based near St. Cloud. The site has also been of academic interest, with recent Carleton College graduate Emma Watson (Class of 2023) completing her comprehensive thesis on the Morton Gneiss. The Morton Gneiss is Archean in origin, with its protolith (original rock) forming around 3.6 billion years ago. Since its formation, it has undergone multiple episodes of metamorphism and deformation, most notably during the Penokean orogeny (~1.85 billion years ago) and later thermal/metamorphic overprinting during the Proterozoic. It is a banded, migmatitic gneiss, showing evidence of both solid-state metamorphism and partial melting (migmatization). The rock features interlayered felsic bands (BH250-118), mafic bands (BH250-118b), and amphibolite (BH250-118c), each representing different compositions, origins, and metamorphic histories. Amphibolite (BH250-118c) is present as lenses or layers within the Morton Gneiss and represents metamorphosed mafic rocks that may have originated as basaltic or gabbroic intrusions, or as volcanic sediments. Amphibolite in this setting is dominated by hornblende and plagioclase, typically lacking quartz. It can occur conformably with the gneissic layering or as discordant bodies, suggesting emplacement as dikes during or before metamorphism. Geologically, the Morton Gneiss is significant because it preserves a record of early Earth crustal evolution, including crust formation, tectonism, and high-grade metamorphism. It forms part of the Minnesota River Valley subprovince, which is itself a key component of the Superior Province of the Canadian Shield. Interestingly, in the past, outcrops of the Morton Gneiss were considered as potential storage sites for radioactive waste, and remnants of that period—including test wells and excavated pits—can still be seen in certain locations. 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 44°49'7.94"N, 95°33'52.44"W Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 246. 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/1tbGznYh1FAhOfRKxgkRgQ41QQxxTq42t/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/13xiGU89DDm8VQ1dU4WuQePR0lxDxCqWA/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1tnMHw5oIbopk88dP7o6nbT_yZUUeRPN7/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1vs9q7m9Uxitd8soiisAWUOcpXp5UFoNQ/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1YYrDK3R59iryYxQBJWIrX0ts_Iysu1b-/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1v3F5vz19z_LijXjMH9b0bH26cgqHF6sL/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1U5ets6zsvvNbK4-Ix5Oq7-SjWXZ1FKxV/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1wP1dBGW3zLn2i409RlmanQMfl-qgRR2-/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1FHy8p7Y2S3QIDGfPCQgYlTy5LjvO-3tX/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bD4xkklyf0aZQyNIcuEKp41_RLVsJtyd/preview" allow="autoplay"></iframe> amphibolite Amphibolitized Intrusion Archean Gneiss Banded Gneiss Canadian Shield Felsic Gneiss gneiss Granitic Protolith High-Grade Metamorphic Rock Leucosome Veins Mafic Gneiss metamorphic Metamorphosed Mafic Rock Migmatitic Gneiss Minnesota Minnesota River Valley Subprovince Morton Morton Gneiss Partial Melting Features Penokean Orogeny Proterozoic Overprinting Quartz-K-feldspar-Plagioclase-Biotite Radioactive Waste Test Site https://bereket-haileab.geology.sites.carleton.edu/files/original/a7d433f0185d26d935d7f4ff5d2d0e12.jpg 43917ce616d7592c79326eeae79ffa5b 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 BH250-119 Subject The topic of the resource Basaltic Andesite/Basaltic Trachyandesite Description An account of the resource Major Minerals; plagioclase; orthoclase; clinopyroxene<br /><br /><span>BH250-119 (collected by Mike Smith, Class of 2929) is classified as either a basaltic andesite or a basaltic trachyandesite, as it plots directly on the boundary line between these two rock types on the Total Alkali-Silica (TAS) diagram. Both rock types are part of the intermediate volcanic spectrum and are prominently exposed in the region around Flagstaff, Arizona, particularly within the San Francisco Volcanic Field—a large and geologically active area in northern Arizona. Basaltic andesite and basaltic trachyandesite are compositionally transitional between basalt and andesite, typically containing 53–57 wt% silica (SiO₂). Mineralogically, they are dominated by plagioclase (often labradorite), with common mafic minerals including clinopyroxene (augite), orthopyroxene (hypersthene), and olivine. Accessory minerals such as magnetite or other oxides may also be present. These rocks commonly exhibit a porphyritic texture, often featuring prominent plagioclase phenocrysts set within a fine-grained groundmass.<br /></span> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=1226666667&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 Flagstaff, AZ, USA, 35.341295, -111.576939 Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 119. Housed at Carleton College in Minnesota. Contributor An entity responsible for making contributions to the resource Mike Smith Type The nature or genre of the resource Thin section, 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=51ddf01eb2a748afb948471f24a4af88" 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=51ddf01eb2a748afb948471f24a4af88">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1sUD-MtrzpQFQeVQggSx2BTbSsWB7aXBA/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1JcmlklZyvtZW1C-BSfXAbneSKFWDJoSo/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1uBWu-6AgaypY8RT5uj-DYfBjA2MXI0Ou/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1lMjTP-GFtNvKbm0M0rAXd_jKpUqpsPXk/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1Lzl2rmRQoeuwsQlWiFhe-cIPC6EjGAWz/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1Lv_Vvy9BLwTZ-O-LvMfvoT3LIJlNao6t/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1fpJ7CSNS36JXKX4LaLAlMxxq_2zPOdjW/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1SMCk7AIBhZHM4ecbVDIA8NAK4Sc6c0pI/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1P59KLY4O_cvafTgJovH1WXmEqxHfu-5l/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1GTeM0UNGr1xoQuTO_gmAM-Iu0av_5wrn/preview" allow="autoplay"></iframe><br />TAS diagram of sample BH250-119. Creator An entity primarily responsible for making the resource Bereket Haileab andesite basalt Basaltic Andesite basaltic trachyandesite Flagstaff Arizona igneous mafic northern Arizona San Francisco Volcanic Field volcanic https://bereket-haileab.geology.sites.carleton.edu/files/original/b00801924613a51d5cffb8e92b81b73e.jpg bd80ff0163bea00b301c010822a77a0d 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-12 Subject The topic of the resource Fluorite Vein Description An account of the resource Major Minerals: calcite, fluorite, aegirine, quartz, olivine Minor Mineral: serpentine Mineralogy Comments: fluorite has purple spots 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: Alta, Utah, USA Nearby Geographic Features: Alta Stock Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 12. 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=043cd8b0846749b5bdb22fb8177cf1d7" 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=043cd8b0846749b5bdb22fb8177cf1d7">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1QxKjNqLO19YzrZApstg9h2KIllzy9H2z/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1A4diE1P-ilug-A6y0yX2BoJ-mZ8ykw-2/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1bajVnZLfnY-7gTJq1pKMxmFByUHjPRJk/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JcXHTSzcwMdSAgTnqvK-y2WwQs6yvxWd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/151ZBZgrb8pqTr0X6RV4GzhtQ0IjbO4V6/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab hydrothermal https://bereket-haileab.geology.sites.carleton.edu/files/original/c88a44e53da3c11ad9c654f7e4e35684.jpg 1604c88ef3b2b1136e3b58811b123a61 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 BH250-120 Subject The topic of the resource Trachydacite Description An account of the resource Major Mineral: plagioclase <br />Minor Mineral: alted mafic minerals<br /><br /><span><span>BH250-120 is a Trachydacite sample (collected by Mike Smith, Class of 1999) from near Flagstaff, Arizona. This rock represents a relatively uncommon but geologically significant volcanic lithology within the San Francisco Volcanic Field (SFVF), a region otherwise dominated by basalt, basaltic andesite, and andesite. Trachyte in this setting reflects a more evolved, silica-undersaturated, alkali-rich magma composition, indicating advanced stages of magmatic differentiation. BH250-120 is a fine-grained, light-colored volcanic rock rich in alkali feldspar—primarily sanidine or anorthoclase—with minor amounts of plagioclase, biotite, amphibole, and pyroxene. Quartz is rare or absent, and the rock contains ~60–65 wt% silica, with elevated concentrations of alkali oxides (Na₂O + K₂O). The texture is typically porphyritic, with large alkali feldspar phenocrysts set in a groundmass that exhibits a trachytic texture, where feldspar laths are flow-aligned due to magmatic movement. In thin section, BH250-120 reveals large phenocrysts of plagioclase feldspar, remnants of what were once mafic minerals and volcanic glass. The original ferromagnesian minerals are now completely altered, and the outlines of amphiboles have been replaced by iron oxides. The flow alignment of the plagioclase feldspars is especially prominent and adds to the evidence of viscous, evolved magma flow during emplacement.<br /><br /></span></span> <p>In this sample, you can observe<span class="apple-converted-space">&nbsp;</span><strong data-start="32" data-end="58"><span style="font-weight: normal;">hornblende dehydration</span></strong>, 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></p> <p data-start="516" data-end="1113">This process commonly produces<span class="apple-converted-space">&nbsp;</span><strong data-start="547" data-end="564"><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 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="945" data-end="960"><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></p> <p data-start="1115" data-end="1572">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="1464" data-end="1491"><span style="font-weight: normal;">disequilibrium features</span></strong>, showing that minerals did not have time to adjust fully to changing conditions.<o:p></o:p></p> <p data-start="1574" data-end="2025" data-is-last-node="" data-is-only-node="">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="1765" data-end="1809"><span style="font-weight: normal;">pre-eruptive degassing and</span> decompression</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></p> <br /><br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=49299193&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: Flagstaff, Arizona, USA GPS Coordinates: 35.253810, -111.623994 Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 120. Housed at Carleton College in Minnesota. Contributor An entity responsible for making contributions to the resource Mike Smith 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=362ead9eca4d49c490bbf052269e4863" 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=362ead9eca4d49c490bbf052269e4863">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1--z9KW7mZLJ-SEGXkg5DcA5NJza2GL9W/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1JHwASoBZnjLP-V6f8AZAq54gZBQWah27/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14PVKVU3szTNemTUEKt1L5mdplxlRFrHN/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ThxABHfQ9DP6aM2Je6nPYAwecXGV3nzx/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1Usqcd6Dsoom1_zkbAJ8d4PVStq2sqk-q/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZI3vi7_LTxFKlsjF0OIv-OBOorKOVvFV/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1IQ1X7__rnbjbBU-dtBjKZhlpUe223BXF/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kgfKf9g4Sdtz0lF15VDVKQF0IE9XnyMz/preview" allow="autoplay"></iframe><br />TAS diagram of smaple BH250-120. Creator An entity primarily responsible for making the resource Bereket Haileab aligned feldspar laths Alkali-Rich Volcanic Rock Altered Mafic Minerals amphibole amphibole breakdown complete alteration dacite disequilibrium texture felsic ferromagnesian minerals fine-grained groundmass Flagstaff Arizona Flagstaff Geology flow alignment Flow-Aligned Feldspar Hornblende hornblende dehydration igneous Iron Oxide Replacement Iron Oxides Magnetite mineral replacement northern Arizona Northern Arizona Volcanism oxide rims partial alteration Phenocrysts plagioclase phenocrysts porphyritic texture Pseudomorph Pyroxene Reaction rims San Francisco Volcanic Field Trachydacite Trachytic Texture volcanic Volcanic glass Volcanic rock https://bereket-haileab.geology.sites.carleton.edu/files/original/8504a1de14e60db1a88e2e7068f8d329.jpg 29c971497a8e02bc39c01b38a3a26d6b 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 Metamorphic Rocks Subject The topic of the resource This collection includes slates, phyllites, schists, gneisses, eclogites, marbles, quartzites, skarns, granulites, and mylonites. 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 BH250-121 Subject The topic of the resource Garnet Staurolite Schist Description An account of the resource BH250-121 was collected near the Ingersoll Mine, Keystone, South Dakota, USA. This sample represents one of the most beautiful rocks—both in hand sample and thin section. It is a classic example of garnet-staurolite schist from the Black Hills region. The protolith is pelitic shale or graywacke, indicated by the presence of aluminum-rich minerals formed during metamorphism. Mineral assemblage includes: Garnet – euhedral to subhedral, commonly poikiloblastic Staurolite – typically twinned and yellow-brown in color, characteristic of amphibolite facies Muscovite, biotite, quartz, and plagioclase – all common matrix minerals Textural features: Schistosity is well-developed, with micas aligned in a distinct foliation Porphyroblasts of garnet and staurolite prominently stand out against the fine-grained groundmass, offering excellent contrast in both hand sample and thin section. This sample is not only geologically significant but also visually striking, making it an outstanding teaching specimen for regional metamorphism and mineral identification. There is a large rock sample in the back of the class room. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant GPS Location: 43°54'11.77"N, 103°27'2.31"W Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 121. 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=e9d442352d804fe2a279f050b667bbee" 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=e9d442352d804fe2a279f050b667bbee">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1E1XVwRfDSY_10wK9ztaXoF5NM-M_ZRtY/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1yIYeAtZsB4HmbzDGCsIiufEgM2yZ56oQ/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1NuIZN8jIqRhHEs5fhZO8912ov4AUCQZi/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZOrdTDYf_RYWOSCPowAwZ683DCS4ZrYE/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ny2DgS3i-6wsihNxNeniZog1TWCDNiNf/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1oMEcfQnlR-3YmuW5Sw0WKGRl_YQkF-mH/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fJhQcRyUrgBucggVZhlUmhP2GlJscY8c/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/19F4zmuzuCmVxLrHVcpRjThOl6XbJKc5i/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1xz-peyWLDgImCJXAL5fL5CH6wBdb8B8w/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1CJjILdhUYtreYCnW2vo67szDKwXYIed2/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1fzs3NsZa8obmVnIaQnHJ31QBJAjkeXYd/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Aluminum-rich metamorphic minerals Amphibolite Facies Black Hills metamorphic core Garnet porphyroblast Garnet-Staurolite Schist Ingersoll Mine Keystone South Dakota geology metamorphic pelitic protolith Poikiloblastic garnet Porphyroblastic texture Regional metamorphism schist Staurolite twinning https://bereket-haileab.geology.sites.carleton.edu/files/original/071d9b53bc6c55c7431ad96c47ca2f90.JPG 50c6be3c7a12e840195e760efab2017a 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 Sedimentary Rocks Subject The topic of the resource This collection includes sandstones, limestones, breccias, conglomerates, dolostones, shales, oolites, and BIF. 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. 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 BH250-122 Subject The topic of the resource Limestone within the Decorah Shale Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Near Rochester MN Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-122. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Hand sample Relation A related resource <iframe width="100%" height="480" src="https://drive.google.com/file/d/1bHf5GQcOth_vCqlsBBtm8QQVLNr6bFlY/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Description An account of the resource The Decorah Shale directly overlies the Platteville Limestone and consists of fine-grained, greenish-gray shale interbedded with occasional carbonate lenses. The outcrop is rich in articulate brachiopods and bryozoans, disarticulated crinoid, gastropods, bivalves, cephalopods, rugose corals, and trilobites. The photo of this sample shows rugose coral. Brachiopods Bryozoans carbonate Cephalopods Crinoids Decorah Shale Fossiliferous Limestone limestone Rugose coral sedimentary Trilobites