metamorphic
Schist (Micaceous)
Mica Schist
Hardness: 3.5-4; Color: Silvery-gray, bronze, or greenish-brown; Luster: Pearly to metallic (silky shimmer); Crystal Structure: Foliated with distinct layering; Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.7–2.8.
- Hardness
- 3
- Color
- Silvery-gray, bronze, or greenish-brown
- Luster
- Pearly to metallic (silky shimmer)
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Physical properties
Hardness: 3.5-4; Color: Silvery-gray, bronze, or greenish-brown; Luster: Pearly to metallic (silky shimmer); Crystal Structure: Foliated with distinct layering; Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.7–2.8.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone at medium grades of pressure and temperature. The original clay minerals recrystallize into large, flat mineral grains like muscovite or biotite.
Uses & applications
Primarily used as a decorative stone in landscaping, flagstone for walkways, and occasionally as a source of mica for industrial insulation or lubricants. It is generally too fragile for high-stress construction.
Geological facts
The word 'schist' is derived from the Greek word 'schizein', meaning 'to split,' referring to how easily the rock can be split along its plates. It often contains garnet 'porphyroblasts', which are well-formed crystals growing within the mica layers.
Field identification & locations
Identify in the field by its 'schistosity'—a sparkly, glitter-like appearance caused by the reflection of light off parallel mica flakes. It will often flake off in small, thin pieces when scratched. Commonly found in mountain belts and Precambrian shield areas.
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