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