metamorphic
Mica Schist
Schist (muscovite/biotite rich regional metamorphic rock)
Hardness: 3.5 to 5 on Mohs scale depending on mineral content. Color: Silvery-gray, greenish-gray, to brownish. Luster: Pearly to sub-metallic shimmer due to aligned mica flakes. Texture: Foliated with prominent schistosity. Cleavage: Perfect basal cleavage in individual mica grains causing planar splitting.
- Hardness
- 3
- Color
- Silvery-gray, greenish-gray, to brownish
- Luster
- Pearly to sub-metallic shimmer due to aligned mica flakes
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Physical properties
Hardness: 3.5 to 5 on Mohs scale depending on mineral content. Color: Silvery-gray, greenish-gray, to brownish. Luster: Pearly to sub-metallic shimmer due to aligned mica flakes. Texture: Foliated with prominent schistosity. Cleavage: Perfect basal cleavage in individual mica grains causing planar splitting.
Formation & geological history
Formed through medium-grade regional metamorphism of precursor shale, mudstone, or clay-rich sedimentary rocks under high temperature and pressure conditions, causing platy mica minerals to align perpendicular to stress directions.
Uses & applications
Used occasionally as decorative dimension stone, flagstone, landcaping rock, and historical building stone. Rich mica schist deposits are sometimes mined for raw industrial mica used in insulation, cosmetics, and paints.
Geological facts
Mica schist gets its characteristic sparkle from flat, platy crystals of muscovite and biotite mica. Small garnet crystals (garnet-mica schist) often grow inside it as porphyroblasts during high-grade metamorphic events.
Field identification & locations
Identified in the field by its distinctive glittering sheen, well-developed parallel layering (schistosity), and tendency to flake off in silvery layers. Commonly found in mountain belts like the Appalachians, Alps, and Scottish Highlands.
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