metamorphic
Schist (Biotite Schist)
Biotite-bearing Schist (K(Mg,Fe)3AlSi3O10(F,OH)2)
Hardness: 2.5-4; Color: Black, charcoal grey, dark brown; Luster: Sub-metallic to vitreous (shimmery); Crystal structure: Monoclinic; Cleavage: Perfect basal (flaky); Specific gravity: 2.8-3.4
- Hardness
- 2
- Color
- Black, charcoal grey, dark brown
- Luster
- Sub-metallic to vitreous (shimmery)
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Physical properties
Hardness: 2.5-4; Color: Black, charcoal grey, dark brown; Luster: Sub-metallic to vitreous (shimmery); Crystal structure: Monoclinic; Cleavage: Perfect basal (flaky); Specific gravity: 2.8-3.4
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks like shale under intermediate pressure and temperature conditions. It typically dates to various orogenic events across geological time.
Uses & applications
Used primarily as decorative stone, in garden landscaping, and occasionally as a minor building stone. In the past, ground mica was used in lubricants and as a filler.
Geological facts
The word schist is derived from the Greek 'schistos', meaning 'split', referring to the ease with which these rocks can be divided into thin sheets along their foliation planes.
Field identification & locations
Identify by its 'schistosity' or platy alignment of mica minerals which creates a characteristic shimmer. Commonly found in mountainous regions or areas with exposed metamorphic basement rock. Collectors look for well-defined mica flakes.
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