metamorphic
Mica Schist
Mica Schist (predominantly Muscovite or Biotite sheet silicates)
Hardness: 3.5-4 (Mohs scale); Color: Silvery-gray, brownish, or metallic; Luster: Pearly to sub-metallic with a strong 'sparkle'; Crystal Structure: Monoclinic (plate-like minerals); Cleavage: Perfect basal cleavage on individual mica flakes; Specific Gravity: 2.7-3.0.
- Hardness
- 3
- Color
- Silvery-gray, brownish, or metallic
- Luster
- Pearly to sub-metallic with a strong 'sparkle'
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Physical properties
Hardness: 3.5-4 (Mohs scale); Color: Silvery-gray, brownish, or metallic; Luster: Pearly to sub-metallic with a strong 'sparkle'; Crystal Structure: Monoclinic (plate-like minerals); Cleavage: Perfect basal cleavage on individual mica flakes; Specific Gravity: 2.7-3.0.
Formation & geological history
Formed through regional metamorphism of shale or mudstone at intermediate temperatures and pressures. This creates coarse-grained foliated textures where minerals like mica grow large enough to be seen by the naked eye. Age varies depending on the specific mountain-building event, ranging from Precambrian to Cenozoic.
Uses & applications
Used primarily in construction as decorative stone, floor tiles, and garden ornaments. Historically used as a source of mica for electrical insulation and heat-resistant windows in ovens. High mica-content schist is also used in the manufacturing of drywall and paint additives.
Geological facts
Mica schist is known for its 'schistosity,' a texture that allows it to be split into thin, flat sheets. The term 'schist' comes from the Greek word 'schizein,' meaning 'to split.' If a specimen contains garnets, it is referred to as Garnet-Mica Schist.
Field identification & locations
Identify it in the field by its distinct silvery glitter and its tendency to flake or peel when scratched with a fingernail or knife. It is common in mountainous regions such as the Appalachian Mountains, the Alps, and the Himalayas. Collectors should look for pieces with large muscovite flakes or embedded garnets.
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