metamorphic
Mica Schist
Mica Schist (primarily Muscovite or Biotite KAl2(AlSi3O10)(OH)2)
Hardness: 2-2.5 on Mohs scale; Color: Silver, grey, or brownish-green; Luster: Pearly to sub-metallic; Structure: Foliated with prominent schistosity; Cleavage: Perfect basal cleavage in individual flakes.
- Hardness
- 2-2
- Color
- Silver, grey, or brownish-green
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 2-2.5 on Mohs scale; Color: Silver, grey, or brownish-green; Luster: Pearly to sub-metallic; Structure: Foliated with prominent schistosity; Cleavage: Perfect basal cleavage in individual flakes.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone at intermediate temperatures and pressures. These conditions cause microscopic clay minerals to recrystallize into large, visible mica flakes.
Uses & applications
Used historically as a building stone (dimension stone) and for flagstones. Muscovite mica is used as an electrical insulator and in the cosmetics industry for shimmer.
Geological facts
Mica schist is known for its 'sparkle.' The word schist comes from the Greek word 'schistos,' meaning 'divided,' referring to the way the rock easily splits into thin plates.
Field identification & locations
Identify by its shiny, glitter-like appearance and plate-like layering (foliation). It is commonly found in mountain ranges such as the Appalachians, Alps, and Himalayas. Collectors look for accessory minerals like Garnet or Staurolite often found within it.
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