metamorphic
Mica Schist
Mica Schist (KAl2(AlSi3O10)(OH)2 / K(Mg,Fe)3AlSi3O10(OH)2)
Hardness: 3.5-4; Color: Silver, gold, brownish-tan; Luster: Pearly to metallic (highly reflective); Crystal structure: Monoclinic (platey); Cleavage: Perfect basal; Appearance: Distinctly foliated and sparkling.
- Hardness
- 3
- Color
- Silver, gold, brownish-tan
- Luster
- Pearly to metallic (highly reflective)
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Physical properties
Hardness: 3.5-4; Color: Silver, gold, brownish-tan; Luster: Pearly to metallic (highly reflective); Crystal structure: Monoclinic (platey); Cleavage: Perfect basal; Appearance: Distinctly foliated and sparkling.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under high pressure and temperature. The mica flakes align perpendicularly to the direction of pressure, creating a foliated texture. Geological age varies greatly by location.
Uses & applications
Used primarily for its aesthetic sparkle in decorative stones, as an insulator in electrical components (mica), or in the cosmetics industry when ground into powder.
Geological facts
The word 'schist' is derived from the Greek word 'schizein', meaning 'to split', referring to the ease with which the rock can be split into thin layers. It is often mistaken for gold by novices due to its brilliant golden reflection.
Field identification & locations
Look for a flaky, layered appearance where the rock sparkles intensely under sunlight. It is common in mountain belts and metamorphic terrains. You can often peel off thin, transparent flakes with a fingernail or knife.
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