https://bereket-haileab.geology.sites.carleton.edu/files/original/62ff355fc836abb40086fc6149a9b55f.jpg e93195744475531a3440858ebe16d91f Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-93 Subject The topic of the resource Gabbro (Stillwater Complex, Montana) Description An account of the resource Major Minerals: Plagioclase, Diopside (clinopyroxene), Enstatite (orthopyroxene) Location: Stillwater Complex, Montana, USA BH250-93 is one of the best teaching samples in this collection for illustrating early plagioclase crystallization in mafic magma systems. Collected from the famous Stillwater Complex of Montana, this specimen represents a classic layered mafic intrusive environment where crystal settling, magma differentiation, and phase equilibria can be studied exceptionally well. The Stillwater Complex is one of the world’s best examples of a large layered mafic intrusion and is often compared to South Africa’s Bushveld Complex because both preserve remarkable records of magmatic differentiation. In thin section, BH250-93 displays a framework of interlocking euhedral plagioclase feldspar crystals that dominate the rock. These feldspars show well-developed crystal faces and clear polysynthetic twinning, indicating that they crystallized early when space was readily available within the magma chamber. The pyroxenes—both diopside (clinopyroxene) and enstatite (orthopyroxene)—occur primarily in interstitial spaces between the feldspar crystals and are noticeably more anhedral. Their irregular crystal boundaries indicate that they crystallized later, after much of the plagioclase framework had already formed. This textural relationship provides an elegant teaching example of a magma whose original composition likely began within the plagioclase primary crystallization field of a simplified plagioclase-pyroxene system. As cooling began, plagioclase nucleated first and grew freely, developing euhedral forms. The remaining melt gradually evolved toward eutectic conditions where both clinopyroxene and orthopyroxene began crystallizing in the remaining pore spaces. This sequence explains why the pyroxenes appear texturally constrained and anhedral. For introductory students, BH250-93 demonstrates how crystal shape reflects crystallization order. For advanced petrology students, it becomes an excellent exercise in reconstructing parental magma composition, equilibrium crystallization pathways, and interpreting simplified phase diagrams. This specimen beautifully demonstrates that texture can preserve the cooling history of a magma long after solidification. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Stillwater, Montana, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-93. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=47fc25b21fc74e57b9103369e37511ab" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=47fc25b21fc74e57b9103369e37511ab">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1VNOld-c1yL6lgAfTBCLZWZNLUgyUB3rc/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/17k2XgdZ2vMXibidp1Ku7YwqaIy-BHl6P/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1OAicQi9JK9h7MxDpq5xHN4HC1N6rJ60O/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1ywAyUihGAd53z8Q5SIyhJcbccnzLZFlr/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/11NgEnv0thJMC4Rp258O1PUgunwwp7cx3/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1S8HxaHDHzjm8CFiqpvQTU2TUL-mPv-OU/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Anhedral pyroxene Bowen’s Reaction Series Clinopyroxene Crystal Growth Sequence Cumulate texture Diopside Enstatite Equilibrium crystallization euhedral plagioclase Eutectic crystallization Fractional crystallization gabbro igneous Igneous Texture Interstitial pyroxene Interstitial Texture Layered Intrusions Layered mafic intrusion mafic Mafic Igneous Petrology Magma crystallization sequence Magmatic Differentiation Montana geology Orthopyroxene Phaneritic texture Phase diagram modeling Phase Equilibria Plagioclase Plagioclase-Pyroxene System plutonic Stillwater Complex Two-Component System