metamorphic
Muscovite Schist
Muscovite (KAl2(AlSi3O10)(OH)2) in Schist
Hardness: 2-2.5 (mica) to 6 (quartz components). Color: Silvery-white to pale green or tan. Luster: Pearly to metallic. Crystal structure: Monoclinic, forms in flat, flaky sheets. Cleavage: Perfect basal cleavage. Specific gravity: 2.7-3.0.
- Hardness
- 2-2
- Color
- Silvery-white to pale green or tan
- Luster
- Pearly to metallic
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Physical properties
Hardness: 2-2.5 (mica) to 6 (quartz components). Color: Silvery-white to pale green or tan. Luster: Pearly to metallic. Crystal structure: Monoclinic, forms in flat, flaky sheets. Cleavage: Perfect basal cleavage. Specific gravity: 2.7-3.0.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks like shale. The high pressure and temperature cause clay minerals to recrystallize into mica flakes that align perpendicular to the direction of pressure.
Uses & applications
Used industrially as an insulator in electrical equipment, as a filler in paints and plastics, and in cosmetics (shimmer). Large, clear sheets were historically used as window panes ('Muscovy glass').
Geological facts
Muscovite is the most common form of mica. It is highly resistant to heat and electricity. It can often be peeled apart into paper-thin, transparent sheets that are surprisingly flexible.
Field identification & locations
Identify in the field by its intense 'sparkle' or 'schistosity' and the ability to flake off transparent bits with a fingernail or knife. Commonly found in mountain ranges and metamorphic belts globally.
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