metamorphic
Biotite Schist
Biotite Schist (containing K(Mg,Fe)3AlSi3O10(OH)2)
Hardness: 2.5-3 (on mica flakes), 6-7 (overall matrix); Color: Dark grey to black with shiny metallic flakes; Luster: Pearly to vitreous; Structure: Foliated (schistose); Cleavage: Perfect basal cleavage in mica crystals.
- Hardness
- 2
- Color
- Dark grey to black with shiny metallic flakes
- Luster
- Pearly to vitreous
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Physical properties
Hardness: 2.5-3 (on mica flakes), 6-7 (overall matrix); Color: Dark grey to black with shiny metallic flakes; Luster: Pearly to vitreous; Structure: Foliated (schistose); Cleavage: Perfect basal cleavage in mica crystals.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under high pressure and temperature conditions. The alignment of mica minerals creates the characteristic foliated texture.
Uses & applications
Primarily used as a specimen for geological study; biotite itself is sometimes used as a filler in paints or drilling muds, though less commonly than muscovite.
Geological facts
The word 'schist' is derived from the Greek word 'schistos', meaning 'split', referring to the ease with which these rocks can be divided into layers.
Field identification & locations
Identify in the field by its distinct layering and the presence of scaly, reflective black mica flakes that can often be peeled off with a fingernail. Common in mountain belts like the Appalachians or Alps.
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