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Mineral qualifiers are important when naming a schist. For example, a quartz-feldspar-biotite schist is a schist of uncertain protolith that contains biotite mica, feldspar, and quartz in order of apparent decreasing abundance. [14] Lineated schist has a strong linear fabric in a rock which otherwise has well-developed schistosity. [10]
Although tremolite is a metamorphic amphibole, it is most commonly derived from highly metamorphosed ultramafic rocks, and thus tremolite-talc schist is not generally considered a variety of amphibolite. A holocrystalline plutonic igneous rock composed primarily of hornblende amphibole is called a hornblendite, which is usually a crystal ...
Some rock types containing chlorite, such as chlorite schist, have minor decorative uses or as construction stone. However, chlorite is a common mineral in clay, which has a vast number of uses. [9] Chlorite schist has been used as roofing granules, the mineral granules adhered to asphalt composition shingles due to the green color.
Granulite (Latin granulum, "a little grain") is a name used by petrographers to designate two distinct classes of rocks. According to the terminology of the French school it signifies a granite in which both kinds of mica (muscovite and biotite) occur, and corresponds to the German Granit, or to the English muscovite biotite granite. This ...
The Brahma Schist consists of amphibolite, hornblende-biotite-plagioclase schist, biotite-plagioclase schist, orthoamphibole-bearing schist and gneiss, and metamorphosed sulfide deposits. As inferred from relict structures and textures, the Brahma Schist is composed of mafic to felsic -composition metavolcanic rocks.
Metamorphic rock formed in these settings tends to shown well-developed foliation. [33] Foliation develops when a rock is being shortened along one axis during metamorphism. This causes crystals of platy minerals, such as mica and chlorite, to become rotated such that their short axes are parallel to the direction of shortening. This results in ...
An igneous rock composed almost entirely of dark mica (biotite or phlogopite) is known as a glimmerite or biotitite. [18] Biotite may be found in association with its common alteration product chlorite. [12] The largest documented single crystals of biotite were approximately 7 m 2 (75 sq ft) sheets found in Iveland, Norway. [19]
Quartz (SiO 2) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid content of the rock. [1] [2] Amphiboles and biotite are common in lesser quantities, while accessory minerals include apatite, magnetite and zircon. [3] [4] In older references tonalite is sometimes used as a synonym for quartz diorite.