metamorphic
Biotite Schist
Biotite Gneissic Schist (K(Mg,Fe)3AlSi3O10(OH)2)
Hardness: 2.5-3 (on mica flakes), Color: Dark brown to black with silvery sheen, Luster: Pearly to submetallic, Texture: Foliated with visible flaky mica grains
- Hardness
- 2
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Physical properties
Hardness: 2.5-3 (on mica flakes), Color: Dark brown to black with silvery sheen, Luster: Pearly to submetallic, Texture: Foliated with visible flaky mica grains
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under high temperature and pressure, typically during mountain-building events. Geological age varies by location, often Proterozoic to Paleozoic.
Uses & applications
Primarily used as an indicator of metamorphic grade in geology. Historically used as an insulator and in ground form as a lubricant or filler in shingles and paints.
Geological facts
Biotite is often called black mica. The shiny flakes are actually very thin sheets that can be peeled away. It is a common constituent of many igneous and metamorphic rocks like granite and gneiss.
Field identification & locations
Identify by its sparkly, flaky appearance and dark color. It can be found in mountain ranges and areas with exposed crystalline basement rock. Collectors look for large, well-defined books of mica flakes.
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