metamorphic
Biotite Schist
Biotite Schist (Rich in K(Mg,Fe)3AlSi3O10(OH)2)
Hardness: 2.5-3.0 (on the Mohs scale for the mica component); Color: Black, dark brown, or dark green; Luster: Pearly to vitreous; Structure: Foliated (schistose) with visible mica flakes; Cleavage: Perfect basal cleavage in individual biotite crystals.
- Hardness
- 2
- Color
- Black, dark brown, or dark green
- Luster
- Pearly to vitreous
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Physical properties
Hardness: 2.5-3.0 (on the Mohs scale for the mica component); Color: Black, dark brown, or dark green; Luster: Pearly to vitreous; Structure: Foliated (schistose) with visible mica flakes; Cleavage: Perfect basal cleavage in individual biotite crystals.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures. This process causes clay minerals to recrystallize into plate-like micas that align perpendicularly to the direction of pressure.
Uses & applications
Used primarily as a geological teaching specimen; occasionally used in the manufacturing of heat-resistant materials, lubricants, or as a filler in paints and plastics.
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 layered or split along its foliation planes. Biotite is often called 'black mica' and is a common rock-forming mineral.
Field identification & locations
Identify in the field by its distinct layered appearance (foliation) and the presence of shiny, dark, flake-like minerals that can be peeled off with a fingernail. It is common in mountain belts and Precambrian shield areas.
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