metamorphic
Mica Schist
Mica Schist (predominantly Muscovite/Biotite)
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray to bronze with metallic flashes; Luster: Pearly to sub-metallic; Structure: Foliated (schistosity); Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.8-3.0.
- Hardness
- 3
- Color
- Silvery-gray to bronze with metallic flashes
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray to bronze with metallic flashes; Luster: Pearly to sub-metallic; Structure: Foliated (schistosity); Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high grade heat and pressure. This transformation usually occurs at convergent plate boundaries over millions of years.
Uses & applications
Used primarily as decorative stone, in construction as fill or flagstone, and historically as a source of mica for electrical insulation and heat-resistant windows.
Geological facts
The word 'schist' is derived from the Greek word 'schistos', meaning 'split', referring to the ease with which the rock can be layered or split. The shimmering effect is caused by the alignment of plate-like mica minerals.
Field identification & locations
Identify by its 'sparkly' or 'glittery' appearance and distinct layers (foliation) that may flake off with a fingernail. Commonly found in Appalachian Mountains and alpine regions. Collectors look for well-defined garnets embedded within the mica matrix.
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