mineral

Muscovite

Muscovite (KAl2(AlSi3O10)(OH)2)

Hardness: 2-2.5 on Mohs scale; Color: Colorless, white, grey, brown, yellowish; Luster: Vitreous, pearly, or silky; Crystal structure: Monoclinic, forms as sheet silicates (phyllosilicates) with perfect basal cleavage yielding extremely thin, flexible elastic sheets; Specific gravity: 2.77-2.88

Hardness: 2-2
Color: Colorless, white, grey, brown, yellowish
Luster: Vitreous, pearly, or silky

Identified July 28, 2026More mineral →

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Physical properties

Formation & geological history

Forms in igneous rocks like granites and pegmatites, in metamorphic rocks such as schists and gneisses, and occasionally in sedimentary rocks as detrital grains. Crystallizes from cooling magmas or during regional metamorphism under moderate to high temperatures and pressures.

Uses & applications

Used in electrical insulators, paints, plastics, drywall joint compound, cosmetics for pearlescent sheen, and as a refractory material.

Geological facts

Muscovite was historically known as 'Muscovy glass' because it was used as a substitute for glass in windows in medieval Russia due to its ability to be split into large, thin, transparent sheets.

Field identification & locations

Easily identified by its perfect basal cleavage allowing it to be peeled into flexible, transparent sheets, and its pearly luster. Commonly found worldwide in pegmatite veins and metamorphic schists.