Muscovite

Muscovite is the most common mica and an important rock-forming silicate with the formula KAl2(AlSi3O10)(OH)2. Its perfect basal cleavage allows it to be split into extremely thin, flexible, transparent sheets, a property that led to its historical use as window glass known as Muscovy glass. The mineral crystallizes in the monoclinic system as tabular or pseudo-hexagonal books, showing a vitreous luster, a colorless streak, and colors from colorless through silver-white to pale green. Its Mohs hardness is 2 to 2.5 and its specific gravity 2.77 to 2.88. Its low hardness of 2 to 2.5 and elastic sheets are shared across the mica group, of which muscovite is the light-colored representative.

Muscovite is the most common mica mineral and an important rock-forming silicate. Its perfect basal cleavage allows it to be split into extremely thin, flexible, transparent sheets. These sheets were historically used as window glass (Muscovy glass).