metamorphic
Mica Schist (with Muscovite mica)
Mica Schist (KAl2(AlSi3O10)(OH)2)
Hardness: 2-2.5 for mica, 6-7 for the rock mass; Color: Silver, gray, or brassy gold; Luster: Pearly to metallic; Crystal structure: Monoclinic (platy sheets); Cleavage: Perfect basal; Specific gravity: 2.8.
- Hardness
- 2-2
- Color
- Silver, gray, or brassy gold
- Luster
- Pearly to metallic
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Physical properties
Hardness: 2-2.5 for mica, 6-7 for the rock mass; Color: Silver, gray, or brassy gold; Luster: Pearly to metallic; Crystal structure: Monoclinic (platy sheets); Cleavage: Perfect basal; Specific gravity: 2.8.
Formation & geological history
Formed by the regional metamorphism of shale or sedimentary mudstone under medium-grade pressure and temperature conditions. It typically dates from various periods depending on regional orogeny.
Uses & applications
Used historically as an insulator in electrical equipment, in joint compounds, as a dusting agent, and sometimes as a decorative stone in landscaping or rustic architecture.
Geological facts
The word schist comes from the Greek word 'schistos' meaning 'split', referring to the ease with which the rock can be divided into layers. Its shiny appearance often leads it to be mistaken for precious metals.
Field identification & locations
Identify by its 'schistosity' (sparkly, parallel layering of visible mica flakes). Common in mountainous regions like the Appalachians or Alps. Collectors look for well-defined flakes and included garnets.
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