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How is mica formed?

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Quick Answer

There is no definitive evidence to fully explain the formation of mica as the process is still under scientific study as of 2015. However, mica formation is said to be closely associated with the lack of orthoclase feldspar in pegmatites, which is where the mineral is predominantly found.

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Full Answer

Mica is an important component in igneous and metamorphic rocks, such as granite and schist. Due to its sparkling physical appearance, the mineral is popularly known by various names, including cat-gold, glist, katzengold, cat-silver and glimmer. Mica, which belongs to the silicate group of minerals, is primarily composed of aluminum silicate and hydroxyl alkalis. Some mica varieties contain iron, lithium, magnesium and the trace elements manganese, fluorine, barium and vanadium.

Mica is generally characterized by its brittleness, which readily splits into thin layers or flat plates along its unidirectional cleavage. This mineral is commonly found as crystalline sheets or slabs in acid pegmatites, which form in areas with minimal earthquake and volcanic activity. The extent to which orthoclase feldspar is absent in acid pegmatites is typical of an abundance of mica in a mineral lode.

Another indication of significant deposits of mica is the high occurrence of tourmaline and degraded feldspar in pegmatites. Some of the common forms of mica include muscovite, phlogopite, biotite, lepidolite and paragonite.

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