muscovita

Muscovite, or muscovite mica, is a silicate mineral in the mica group with a layered, sheet-like structure. Its chemical formula is commonly written as KAl2(AlSi3O10)(OH)2, with fluorine sometimes substituting for hydroxyl in some samples. The mineral crystallizes in monoclinic symmetry and forms flexible, transparent sheets that exhibit perfect cleavage along the basal {001} plane.

In hand specimens, muscovite is typically colorless or pale brown in its pure form and can be transparent to translucent. The sheets have a pearly luster on cleavage faces. Mohs hardness is about 2–2.5, and the specific gravity ranges roughly from 2.76 to 3.0.

Muscovite occurs in a variety of geological settings, including granitic and pegmatitic rocks and low- to medium-grade metamorphic rocks such as schists. It forms during crystallization of felsic magmas or by alteration of aluminous sediments and is commonly associated with quartz, feldspar, tourmaline, and beryl.

The name muscovite derives from its historical exploitation in the Muscovy region around Moscow, Russia. It is also known by the common name mica. In addition to muscovite, mica group minerals include phlogopite, biotite, and lepidolite, which differ in composition.

Muscovite is mined as an industrial mineral and is valued for its dielectric strength, thermal stability, and resistance to weathering. It is used as electrical insulation in capacitors and other components, as heat-resistant window panes in the past, and as a filler and pigment in paints, plastics, and cosmetics. Collectors prize clear crystals.