![Biotite Schist (Biotite Mica Schist [K(Mg,Fe)3AlSi3O10(OH,F)2]) — metamorphic](https://media.rockidentification.com/d56dfa7c-66f4-4178-aebe-65fa4ee36c5f-compressed.jpg)
metamorphic
Biotite Schist
Biotite Mica Schist [K(Mg,Fe)3AlSi3O10(OH,F)2]
Hardness: 2.5-3.0 on Mohs scale; Color: Black, dark brown, or dark green with silvery highlights; Luster: Vitreous to pearly; Crystal Structure: Monoclinic with perfect basal cleavage; Specific Gravity: 2.8-3.4
- Hardness
- 2
- Color
- Black, dark brown, or dark green with silvery highlights
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 2.5-3.0 on Mohs scale; Color: Black, dark brown, or dark green with silvery highlights; Luster: Vitreous to pearly; Crystal Structure: Monoclinic with perfect basal cleavage; Specific Gravity: 2.8-3.4
Formation & geological history
Formed through regional metamorphism of clay-rich sedimentary rocks (like shale) under high pressure and temperature. This process aligns the mica crystals into a foliated, sheet-like texture known as schistosity.
Uses & applications
Used primarily as an insulating material in electrical components due to its heat resistance. Smaller ground-up versions are used in paints, joint compounds, and as a filler in rubber and plastics.
Geological facts
Biotite is often called 'Black Mica.' The individual sheets are flexible but break easily. It is one of the most common silicate minerals found in the Earth's crust.
Field identification & locations
Identify by its sparkly, 'glittery' appearance and its tendency to flake off into thin, flexible sheets with a fingernail. Commonly found in mountain ranges and metamorphic terrains.
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