metamorphic
Muscovite Schist with Quartz
Muscovite (KAl2(AlSi3O10)(OH)2) in Quartz Matrix
Hardness: 2-2.5 (mica) / 7 (quartz). Color: Silvery-white to golden sheets in tan/gray matrix. Luster: Vitreous to pearly/metallic. Crystal structure: Monoclinic (sheets). Cleavage: Perfect basal.
- Hardness
- 2-2
- Color
- Silvery-white to golden sheets in tan/gray matrix
- Luster
- Vitreous to pearly/metallic
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Physical properties
Hardness: 2-2.5 (mica) / 7 (quartz). Color: Silvery-white to golden sheets in tan/gray matrix. Luster: Vitreous to pearly/metallic. Crystal structure: Monoclinic (sheets). Cleavage: Perfect basal.
Formation & geological history
Formed through the regional metamorphism of pelitic rocks (shales or mudstones) under high temperature and pressure. The mica crystals align perpendicularly to the direction of pressure, creating a foliated texture.
Uses & applications
Used as an electrical insulator, in high-heat industrial furnace windows, as a filler in paints and plastics, and as a cosmetic glitter (mica).
Geological facts
Muscovite was historically used as a glass substitute in Russia, known as 'Muscovy glass.' Large sheets are highly flexible and can be peeled into paper-thin, transparent layers.
Field identification & locations
Identify in the field by its characteristic 'sparkle' even in low light and its ability to be flaked off with a fingernail. Commonly found in mountain ranges such as the Appalachians or the Alps.
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