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Mica's value is based on its unique physical properties: the crystalline structure of mica forms layers that can be split or delaminated into thin sheets usually causing foliation in rocks. These sheets are chemically inert, dielectric , elastic, flexible, hydrophilic, insulating, lightweight, platy, reflective, refractive, resilient, and range ...
Muscovite is the most common mica, found in granites, pegmatites, gneisses, and schists, and as a contact metamorphic rock or as a secondary mineral resulting from the alteration of topaz, feldspar, kyanite, etc. It is characteristic of peraluminous rock, in which the content of aluminum is relatively high. [8]
Phlogopite is an important and relatively common end-member composition of biotite. Phlogopite micas are found primarily in igneous rocks, although it is also common in contact metamorphic aureoles of intrusive igneous rocks with magnesian country rocks and in marble formed from impure dolomite (dolomite with some siliclastic sediment).
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]
The composition of the rock must permit formation of abundant platy minerals. For example, the clay minerals in mudstone are metamorphosed to mica, producing a mica schist. [18] Early stages of metamorphism convert mudstone to a very fine-grained metamorphic rock called slate, which with further metamorphism becomes fine-grained phyllite ...
Fuchsite, also known as chrome mica, is a chromium (Cr)-rich variety of the mineral muscovite, belonging to the mica group of phyllosilicate minerals, with the chemical formula K(Al,Cr) 2 (AlSi 3 O 10)(OH) 2. [2] Trivalent chromium replaces one of the aluminium (Al) atoms in the general muscovite formula producing the apple green hue ...