The arenaceous bands that are present in the previously described locations are absent in this rock. This feature suggests formation of the protolith of AS17 in deeper water conditions with a … sillimanite is a characteristic mineral of high grade metamorphic rocks; ... schist, and gneiss—are formed during regional metamorphism. These start out originally with clay minerals and as a result of metamorphism, Alumina rich minerals like micas, chlorite, garnet, kyanite, sillimanite and andalusite form. Question: 1.If A Schist If Found To Contain Graphite, We Can Conclude That Its Protolith Had Abundant _____. The protolith is either a mafic igneous rock or graywacke. Indiana Does Not Have Natural Exposures Of Metamorphic Rock, But Occasional Boulders Of Metamorphic Rocks Can Be Found On The Surface. As the rocks become heated at depth in the Earth during regional metamorphism they become ductile, which means they are relatively soft even though they are still solid. It usually forms on a continental side of a convergent plate boundary where sedimentary rocks, such as shales and mudstones, have been subjected to compressive forces, heat, and chemical activity. General terms used to describe the chemical composition of both the protolith and the resulting metamorphic rock are: Pelitic Alumina rich rocks, usually shales or mudstones. ... Garnet muscovite schist. Schist is a foliated metamorphic rock made up of plate-shaped mineral grains that are large enough to see with an unaided eye. Sillimanite fibers (variety fibrolite), in a biotite–sillimanite–muscovite schist. Muscovite and sillimanite vary with metamorphic grade. Accessory minerals are iron-titanium oxides, zircon, sphene, and apatite. Compared to AS79 and AS27, AS17 is dominated by sillimanite (>25 vol%). Microcline is an essential constituent of the quartzites and schists and serves to distinguish the Setters rocks from the plagioclase-rich schists and gneisses of the Wissahickon Formation. Schist is a medium-grained strongly-foliated crystalline metamorphic rock, formed by dynamic metamorphism, that can be readily split into thin flakes or slabs due to the well-developed parallelism of more than 50% of the minerals present, particularly those of lamellar or elongate prismatic habit, e.g., mica and amphiboles. Muscovite crystals are visible and silvery, garnets occur as large dark porphyroblasts. Sillimanite fibers can be included in many minerals, and can survive retrograde metamorphism in garnet and quartz. • Sillimanite zone. Schists and gneisses with sillimanite, biotite, muscovite, uartz, plagioclase, garnet, and perhaps staurolite. Assuming a mudstone protolith, the transformation to schist occurs at temperatures between A Iron B Aluminum C Quartz D Carbon Feldspar 2. In medium-grade rocks sillimanite is typically of this fibrous variety. Sillimanite is colorless, and has relief much higher than muscovite. What is Schist?