muscovite

noun

A potassium aluminum silicate mineral, KAl2(AlSi3O10)(OH)2, the most common form of mica, which ranges from colorless or pale yellow to gray and brown, has a pearly luster, and is used as an insulator.

noun

A pale brown mineral of the mica group, being a basic potassium aluminosilicate with the chemical formula KAl2(Si3Al)O10(OH,F)2; used as an electrical insulator etc.