Muskovit

Muscovite, also known as white mica, is a phyllosilicate mineral in the mica group. Its chemical formula is KAl2(AlSi3O10)(OH)2, representing a hydrated potassium aluminum silicate. Muscovite forms as sheet silicate minerals with perfect basal cleavage, allowing it to be split into thin, flexible transparent sheets. Color is typically colorless, white, or pale brown; it can be transparent to translucent and exhibits a vitreous luster. The mineral has a Mohs hardness of 2–2.5 and a specific gravity of about 2.8–3.0.

Geologic occurrence: Muscovite is common in granitic rocks and pegmatites, as well as metamorphic rocks such as schists and gneisses, where it forms from the alteration of potassium-bearing feldspars or crystallization from hydrous siliceous magmas. It often occurs in large crystals or as scales and flakes in mineral assemblages, and it is the light-colored mica that distinguishes it from the darker biotite.

Uses: Due to its perfect cleavage, chemical stability, and high dielectric strength, muscovite has been widely used as an insulating material in electrical equipment, heat-resistant barriers, and as a filler in paints and cosmetics. Historically, very large, transparent sheets were used in place of glass for windows in some regions, giving rise to the attribute “Muscovy glass.”

Etymology: The name muscovite derives from Muscovy (Moscow), where it was historically mined in large, clear crystals. It is commonly referred to as white mica.