metamorphic
Muscovite Mica (with Schist)
Muscovite - KAl2(AlSi3O10)(OH)2
Hardness: 2-2.5; Color: Silvery, brassy, or brown; Luster: Pearly to metallic; Crystal structure: Monoclinic; Cleavage: Perfect basal (peels into thin sheets); Specific Gravity: 2.76–3.00
- Hardness
- 2-2
- Color
- Silvery, brassy, or brown
- Luster
- Pearly to metallic
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Physical properties
Hardness: 2-2.5; Color: Silvery, brassy, or brown; Luster: Pearly to metallic; Crystal structure: Monoclinic; Cleavage: Perfect basal (peels into thin sheets); Specific Gravity: 2.76–3.00
Formation & geological history
Formed during regional metamorphism of clay-rich sedimentary rocks (like shale or mudstone) at medium-to-high temperatures and pressures. Most common in mica schists and pegmatites.
Uses & applications
Used as an electrical insulator in electronics, in drywall joint compounds, as a filler in plastics and paint, and in cosmetics (eye shadow/lipstick) for its pearlescent shimmer.
Geological facts
Muscovite was historically used as a replacement for glass in windows in medieval Russia, leading to its name 'Muscovy-glass'. It is highly resistant to heat and chemicals.
Field identification & locations
Identify by its 'book' of thin, flexible, transparent or silvery sheets that can be easily peeled off with a fingernail. Found globally in metamorphic belts like the Appalachians or the Himalayas.
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