metamorphic
Biotite Schist
Schist (Biotite-dominated)
Hardness: 2.5-3 (for mica flakes); Color: Black, dark brown, or dark grey; Luster: Sub-metallic to pearly; Structure: Foliated with visible flakes; Cleavage: Perfect basal cleavage on individual mica crystals.
- Hardness
- 2
- Color
- Black, dark brown, or dark grey
- Luster
- Sub-metallic to pearly
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Physical properties
Hardness: 2.5-3 (for mica flakes); Color: Black, dark brown, or dark grey; Luster: Sub-metallic to pearly; Structure: Foliated with visible flakes; Cleavage: Perfect basal cleavage on individual mica crystals.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone at intermediate temperatures and pressures. This process occurs during mountain-building events (orogenies) where sedimentary rocks are buried and compressed.
Uses & applications
Primarily used as a decorative stone in landscaping, as a source of mica for electrical insulation, and as a geological specimen for study.
Geological facts
The word 'schist' comes from the Greek word 'schizein', meaning 'to split', referring to how easily the rock can be split along its flat mineral planes. The sparkling appearance is due to the alignment of mica minerals.
Field identification & locations
Identifiable by its 'schistose' texture, where minerals are oriented in a parallel fashion giving it a flaky, glittering appearance. Common in metamorphic belts such as the Appalachian or Alpine ranges. Collectors look for well-defined flakes and interesting accessory minerals like garnet.
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