https://bereket-haileab.geology.sites.carleton.edu/files/original/b165dd5f2e63f575257813b1e70d62d8.jpg 3f1cfbf1e23be18dd16023bb8867004a https://bereket-haileab.geology.sites.carleton.edu/files/original/2c4d90ee62c7128f26c3ae35a0434190.jpg 55591d9c5a5a795b71192539e8ea7a50 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Igneous Rocks Subject The topic of the resource This collection covers both volcanic and intrusive rocks, including rhyolites, granites, diorites, andesites, basalts, gabbros, diabases, pumices, obsidians, syenites, phonolites, peridotites, carbonatites, dacites, trachyte, dunites, xenoliths, ignimbrites, and pegmatites. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs, chemical analyses (major elements, trace elements and REE analyses for selected samples). Thin section and hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-41 Subject The topic of the resource Dunite Description An account of the resource Major Mineral: forsterite, olivine Minor Minerals: serpentine, magnetite Texture: equigranular olivine BH250-41 is a dunite from Balsam, composed almost entirely of forsterite-rich Olivine. It is one of the most visually striking rocks, both in hand sample and especially in thin section. Under crossed polars, the olivine grains display vivid second-order interference colors. Well-oriented grains cut perpendicular to the c-axis yield excellent biaxial interference figures, with a 2V angle close to 90°, making the mineral appear nearly optically neutral. In this orientation, the isogyre forms a straight line that rotates smoothly about the optic axis—an ideal demonstration for teaching optical mineralogy. On the Olivine–Orthopyroxene–Clinopyroxene (Ol–Opx–Cpx) ternary diagram used for ultramafic igneous rock classification, dunite plots near the olivine apex because it contains more than 90% olivine, with only minor pyroxene if present. BH250-41 would therefore plot very close to the Ol corner of the diagram, firmly within the dunite field. This position reflects its highly magnesium-rich, mantle-derived composition and distinguishes it from harzburgite, lherzolite, and pyroxenite fields that contain greater proportions of pyroxenes. Optically, olivine exhibits strong birefringence, producing bright second-order rainbow-like interference colors. It is biaxial with a 2V angle of approximately 90°, and in favorable orientations may appear nearly optically neutral. This sample provides excellent teaching examples for selecting grains that produce an optic-axis interference figure and for demonstrating the difference between biaxial and uniaxial behavior under the microscope. BH250-41 also shows evidence in some thin sections of later metamorphic or alteration reactions, where primary olivine has begun to break down along fractures or grain margins. Common reactions include hydration to Serpentine or talc-bearing assemblages, recording fluid infiltration after crystallization. These secondary textures provide an excellent contrast between pristine mantle olivine and later alteration during tectonic uplift and weathering. A simplified serpentinization reaction is: 3(MgFe)2SiO4 (forsterite) + 2H2O + 2O2 → 2Mg3Si2O5(OH)4 (serpentine) + Fe3O4 (magnetite) <iframe width="1800" height="100" src="https://docs.google.com/spreadsheets/d/e/2PACX-1vS4nyqCmZQGn3t6vX4g4nhDPwHMBaKrigt1LaY2pykWbBGXB1wNb6FYArx625I-JTtD7lyg4uz1OS1r/pubhtml?gid=981347482&single=true&widget=true&headers=false"></iframe> Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-41. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=426a8f55a4dd483ca317808ef82f20b1" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe> View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=426a8f55a4dd483ca317808ef82f20b1">here</a> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1jl-5KZUFAbm3UuhI4czX0CYXcsifXOx_/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1XNRniVB7aQWWoA32Awlp84vfqnY4pQjf/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1JxfcXWHXAREtxcQbCNqg2jwhizTYm1gS/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1-kPFzgN1RKuRHHMx5zRVGLUSgrgEkpZ9/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1TMNilt8f60JiiP_3EX-Dv4xx1iqjWLqZ/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1bjNP6Carp4RV_n0Oa4LwSaLjgoXAJyHQ/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1SSMdVlf18yv7Ym6pMgNjbcEWnzivo9ls/preview" allow="autoplay"><iframe width="100%" height="480" src="https://drive.google.com/file/d/16puBbmOxWiVoP3uob8vl77dopCZMb-TN/preview" allow="autoplay"></iframe></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1hAKVyzvfRGUrVR48Gz_x8tlaJhnA22e2/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/19de2VzZluIHRhS1XeGj1o698koJ1a54B/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1HGpg9JcT-Yw95b5cSDeZKxw6cpXmymYI/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/11TP06iGOAdc7PzLO_fcPOsIGu86wDL1k/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1pRgBMlIT55SDEiEBJsTN_J3uxKULfKOZ/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/18RkeyPoKqbBhrd9xUctkuQyMvWJgiyCe/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1ecsjbkhjcqomvTr9iMPHCABFNW65KHR6/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1TFMweiUFlfx_CZdr5konqpY3688xrU0R/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1NKZYYB89d5aDJXEw2IHZCQiprJyzeJCz/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1FRACWu5QIyv1cTH6sRVVwMcj3W2S-k7k/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1RvzxN4kC6bCy5rj0GR7W0Y0vy1fXgaAl/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1kHxXUzDP6nQgZd82XaIicz3EUJ_KH_Z6/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/16puBbmOxWiVoP3uob8vl77dopCZMb-TN/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Balsam, North Carolina, USA 2V ~90° 2V angle 2V measurements Balsam Balsam NC biaxial Biaxial Mineral biaxial neutral cumulate cumulate rock dunite equigranular euhedral Fo-rich olivine forsterite granular texture high relief igneous igneous rock classification Interference Colors interference figure Isogyre Magnetite mantle derived mantle rock mantle xenolith mantle-derived magma Mg rich olivine North Carolina Ol-Opx-Cpx classification olivine olivine peridotite olivine-rich rock optic axis figure optically neutral orientation peridotite peridotite suite plutonic Serpentine Serpentinization talc alteration ultrabasic ultramafic Ultramafic rock upper mantle USA