metamorphic
Biotite Schist
Biotite-rich Schist
Hardness: 2.5–3 (for biotite flakes); Color: Black, dark brown, or dark grey; Luster: Pearly to vitreous (often sparkly or shiny due to mica); Structure: Foliated with visible mica alignment; Cleavage: Perfect basal cleavage in individual flakes.
- Hardness
- 2
- Color
- Black, dark brown, or dark grey
- Luster
- Pearly to vitreous (often sparkly or shiny due to mica)
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Physical properties
Hardness: 2.5–3 (for biotite flakes); Color: Black, dark brown, or dark grey; Luster: Pearly to vitreous (often sparkly or shiny due to mica); Structure: Foliated with visible mica alignment; Cleavage: Perfect basal cleavage in individual flakes.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks like shale or igneous rocks at medium grades of pressure and temperature (greenschist to amphibolite facies).
Uses & applications
Used primarily as decorative stone, in geological education, and occasionally as a filler in construction materials if found in large quarry quantities.
Geological facts
The 'sparkly' appearance is caused by the alignment of thin, sheet-like mica minerals. It is part of a metamorphic sequence that progresses from slate to phyllite, then schist, and finally gneiss.
Field identification & locations
Identify by its 'schistosity' or layering and the prominent shiny black flakes that can often be peeled off with a knife. Common in mountainous regions with a history of plate collisions.
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