mineral

Muscovite Mica (Granitic Pegmatite)

Muscovite - KAl2(AlSi3O10)(OH)2

Hardness: 2.5 on Mohs scale; Color: Silvery-white to light tan; Luster: Pearly to Vitreous; Crystal Structure: Monoclinic (platy/flaky); Cleavage: Perfect basal cleavage, allowing it to split into extremely thin, flexible sheets.

Hardness: 2
Color: Silvery-white to light tan
Luster: Pearly to Vitreous

Identified March 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous and metamorphic environments, most commonly in granitic pegmatites. The thin, tabular crystals form during the slow cooling of magma at depth or through high-grade regional metamorphism of clay-rich rocks.

Uses & applications

Used widely in the electronics industry as a thermal and electrical insulator. It is also used in cosmetics (as 'mica' for shimmer), paints, joint compounds, and high-temperature furnace windows.

Geological facts

Before glass was widely available, large sheets of muscovite (called 'Muscovy-glass') were used as windows in Russia. It is heat-resistant up to about 700°C, making it an ideal material for viewing ports in old wood stoves.

Field identification & locations

Identify in the field by its 'books' of thin, transparent, or silvery sheets that can be peeled away with a fingernail. Commonly found in granitic outcrops, particularly in mountain ranges like the Appalachians, Urals, or the Himalayas.

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