https://bereket-haileab.geology.sites.carleton.edu/files/original/eb502a56801de4c073995df65023199f.jpg 3433a393cfb12e99cd4cc84b773c99f3 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 BH250-227a Subject The topic of the resource Ankaramite Description An account of the resource Major Minerals: diopside, olivine, plagioclase <br />Minor Minerals: oxides<br /><br /> <p>BH250-227a — Ankaramite (Hawaii)</p> <p>BH250-227a is a striking example of ankaramite, a rare variety of mafic volcanic rock distinguished by its unusually high abundance of large mafic phenocrysts—especially clinopyroxene (diopside/augite) and olivine—set within a much finer-grained volcanic groundmass. This specimen from Hawaii preserves the classic porphyritic texture that makes ankaramites so visually distinctive: large, well-formed crystals are suspended in a dark, fine-grained matrix composed of microlitic plagioclase, pyroxene, volcanic glass or cryptocrystalline material, and minor oxides. In hand sample and thin section, the rock immediately stands out because the phenocrysts appear almost overcrowded relative to the finer matrix, reflecting a magma that began crystallizing significant amounts of mafic minerals prior to eruption.</p> <p>The rock is composed primarily of diopside, olivine, and plagioclase, with minor opaque oxides. The thin sections beautifully document this mineral assemblage. Large euhedral to subhedral diopside phenocrysts are abundant and display bright second-order interference colors under crossed polars. Many crystals show internal fracturing and minor resorption textures, suggesting that they experienced magmatic transport and decompression prior to final eruption. Some pyroxene grains appear clustered together in glomerocrystic aggregates, indicating that crystals may have accumulated within a magma chamber before eruption. The large, brightly colored grains visible in crossed polars are excellent examples of clinopyroxene birefringence and make this sample especially useful for teaching optical mineralogy.</p> <p>Olivine phenocrysts are also prominent and occur as larger fractured crystals, some showing irregular embayed margins that may reflect magmatic corrosion or reaction with surrounding melt. In volcanic rocks, olivine commonly crystallizes early because of its high-temperature stability, and its presence indicates a relatively primitive magma derived from the mantle. Some olivine grains may show early alteration along fractures or grain margins, which is common when olivine interacts with later fluids or weathering processes.</p> <p>The groundmass is dominated by abundant tiny plagioclase microlites, visible in plane-polarized light as densely packed feldspar laths that create a pilotaxitic to intergranular texture. These microlites record rapid cooling after eruption, contrasting sharply with the much slower growth history of the larger phenocrysts. Minor opaque oxides likely represent magnetite or titanomagnetite and record iron-rich crystallization during the later stages of magma evolution.</p> <p>Ankaramite is a relatively uncommon volcanic rock type and is typically associated with alkaline basaltic magmatism in ocean island settings, continental rifts, and some arc environments. The name originates from the Ankaratra volcanic field of Madagascar, which is regarded as the historical type locality from which the rock name was derived. The term has traditionally been used for olivine- and clinopyroxene-rich porphyritic basalts with unusually high modal abundances of large phenocrysts. Modern petrologists sometimes classify these rocks more broadly within alkaline basalt suites, but the term remains widely used in teaching collections because it highlights this distinctive texture and mineral assemblage.</p> <p>The Hawaiian occurrence is particularly interesting because Hawaii is dominated by mantle plume volcanism associated with the Hawaiian hotspot. Primitive melts rising from deep mantle sources can preserve high-temperature minerals such as olivine and clinopyroxene, and ankaramites represent some of the more crystal-rich expressions of these magmas. Their abundance of early-formed crystals may reflect magma chamber accumulation, rapid ascent of crystal-rich melts, or eruption of relatively primitive magmas before extensive fractional crystallization occurred.</p> <p>This sample is especially valuable in teaching because it demonstrates multiple important igneous concepts at once: mantle-derived magma generation, phenocryst formation, crystal accumulation, volcanic groundmass textures, and the relationship between mineral stability and cooling history. The contrast between large phenocrysts and fine-grained matrix makes it an outstanding thin section for introducing students to porphyritic volcanic textures.</p> <br /><iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=457777539&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: Hawai'i, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 227a. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Date A point or period of time associated with an event in the lifecycle of the resource 2022 Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=fc3adc215e0a427ba8b43606b3e9c55b" 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=fc3adc215e0a427ba8b43606b3e9c55b">here</a><a href="https://carleton.maps.arcgis.com/home/item.html?id=d89ba2f360e34742ad1ab40da21056d5"></a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1m5EZztM862zevog7WnwlKdO3pLNmqAtS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kBIqXFPXGlNHfmzfYv0gIEYxxRTeJQQ_/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1dhj6YWpIPz4oatp4GFNvARJHyJo-wRiw/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1csfCRuGbFBE2NWVFMTh_V71WGpaQun78/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1eGARRT_k14sHutT4YiKbgoDrHpj-H1Yd/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OAlI2rBM8kFJ2U438o7S8zWCZ5rUUtdO/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1exR38iq3RamCV1TAEfDpUZeGAjffFe76/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1-fV_qrnOdVFNdo5wdU6PtTpHQvjM3_Jp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1a8dnVDPHPU51t0iqXP-fz8_q1ZPK7FKS/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1E8f6apoxbPoELmTtyU7tWQjSpb8Cgmyw/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OCIWjMhQOgmgo5sbCF9WYJ_BVGtRTjO9/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab alkaline basalt Ankaramite basanite Diopside glomerocrysts Hawaii volcanism Hawaiian hotspot igneous Madagascar mafic mantle plume volcanism olivine Porphyritic basalt volcanic