metamorphic
Mica Schist
Mica Schist (Quartz-Biotit-Muscovite Schist)
Hardness: 3.5–5 (Mohs), Color: Grey, silver-tone, brownish-gold, Luster: Silky to pearly/metallic due to mica flakes, Crystal structure: Foliated, Cleavage: Excellent basal cleavage in mica flakes, Specific gravity: 2.7–2.8
- Hardness
- 3
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Physical properties
Hardness: 3.5–5 (Mohs), Color: Grey, silver-tone, brownish-gold, Luster: Silky to pearly/metallic due to mica flakes, Crystal structure: Foliated, Cleavage: Excellent basal cleavage in mica flakes, Specific gravity: 2.7–2.8
Formation & geological history
Formed through the regional metamorphism of shale, mudstone, or claystone at intermediate to high grades. Platy minerals like mica align under pressure, creating a foliated texture. Most date back to major mountain-building events over hundreds of millions of years.
Uses & applications
Used as building stone, decorative landscaping rock, and occasionally as a source for graphite or garnets found within. Finely ground mica from schist is used in glitters, paints, and cosmetics.
Geological facts
The word 'schist' comes from the Greek word 'schistos,' meaning 'to split,' referring to how easily the rock can flake along its foliation planes. It is the bridge in the metamorphic sequence between phyllite and gneiss.
Field identification & locations
Identify by its sparkly, flaky appearance and distinct layering (foliation). It is extremely common in the Appalachian Mountains, Alps, and Scottish Highlands. Collectors look for 'garnet schists' where dark red garnet crystals are embedded in the mica matrix.
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