metamorphic
Mica Schist
Foliated Metamorphic Rock (Schist)
Hardness: 3.5–4 on Mohs scale; Color: Silvery-gray, tan, or brown; Luster: Pearly to metallic (very sparkly); Crystal structure: Platy/sheet-like; Cleavage: Excellent basal cleavage in mica grains; Specific gravity: 2.7–2.8
- Hardness
- 3
- Color
- Silvery-gray, tan, or brown
- Luster
- Pearly to metallic (very sparkly)
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Physical properties
Hardness: 3.5–4 on Mohs scale; Color: Silvery-gray, tan, or brown; Luster: Pearly to metallic (very sparkly); Crystal structure: Platy/sheet-like; Cleavage: Excellent basal cleavage in mica grains; Specific gravity: 2.7–2.8
Formation & geological history
Formed through high-grade regional metamorphism of clay-rich sedimentary rocks like shale. Under high heat and pressure, small mica flakes grow and align, creating a characteristic layering called schistosity.
Uses & applications
Used historically as a building stone or for flagstones. Today, it is mostly used in the manufacture of flake mica for electrical insulation, filler in rubber/plastic, and occasionally in the cosmetics industry for its sparkle.
Geological facts
The word 'schist' is derived from the Greek word 'schizein', which means 'to split,' referring to the ease with which the rock can be split into thin plates. It often contains larger garnets embedded within the mica layers.
Field identification & locations
Identify in the field by its distinct 'shimmer' or sparkle in sunlight and its tendency to peel or flake into thin sheets. It is commonly found in mountain belts and Precambrian shields worldwide.
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