metamorphic
Muscovite Schist
KAl2(AlSi3O10)(OH)2 (Muscovite) in Schist Matrix
Hardness: 2-3 (muscovite) to 6-7 (quartz/matrix); Color: Silver, gold, or brassy luster on mica plates, brownish-tan rind; Luster: Pearly to metallic; Crystal structure: Monoclinic (sheet-like layers); Cleavage: Perfect basal cleavage.
- Hardness
- 2-3 (muscovite) to 6-7 (quartz/matrix)
- Luster
- Pearly to metallic
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Physical properties
Hardness: 2-3 (muscovite) to 6-7 (quartz/matrix); Color: Silver, gold, or brassy luster on mica plates, brownish-tan rind; Luster: Pearly to metallic; Crystal structure: Monoclinic (sheet-like layers); Cleavage: Perfect basal cleavage.
Formation & geological history
Formed through regional metamorphism of clay-rich sedimentary rocks (pelites) such as shale. Under high pressure and moderate temperature, minerals recrystallize into flat, parallel sheets that create a shiny, platy texture.
Uses & applications
Used as an electrical insulator, in cosmetics (for shimmer), in joint compounds, and as a filler in plastics and paint. Shiny specimens are popular for educational purposes and amateur mineral collecting.
Geological facts
Muscovite was once used as a replacement for glass in windows in medieval Russia, leading to the name 'Muscovy-glass.' Its reflective properties make it a key ingredient in many high-end makeup products.
Field identification & locations
Identify by its 'schistosity'—the alignment of reflective, flaky mineral grains that peel away in thin sheets. Found in mountain belts like the Appalachians or Himalayas. To identify in the field, look for a 'glittery' appearance on a freshly broken surface.
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