metamorphic
Mica Schist
Muscovite/Biotite Schist
Hardness: 3.5-4; Color: Silvery-gray to brownish-tan; Luster: Pearly to metallic (submetallic); Crystal structure: Foliated (schistosity); Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7-2.9
- Hardness
- 3
- Color
- Silvery-gray to brownish-tan
- Luster
- Pearly to metallic (submetallic)
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Physical properties
Hardness: 3.5-4; Color: Silvery-gray to brownish-tan; Luster: Pearly to metallic (submetallic); Crystal structure: Foliated (schistosity); Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7-2.9
Formation & geological history
Formed through regional metamorphism of shale or mudstone under intermediate to high temperature and pressure. This process causes fine-grained clay minerals to recrystallize into large, visible plate-like mica crystals.
Uses & applications
Used historically as a decorative stone in construction and for heat insulation; occasionally used as a filler in paints or as a substrate for garden ornaments. Limited industrial value due to its tendency to flake.
Geological facts
The word 'schist' is derived from the Greek word 'schistos', meaning 'pliable' or 'easily split'. Schist is known for its distinct sheen, often referred to as 'schistosity', caused by the preferred orientation of mica grains.
Field identification & locations
Identify in the field by its distinct glittering or sparkly appearance and foliated texture that allows it to be split into thin flakes. Common in mountain ranges and metamorphic shields like the Appalachians or Alps.
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