metamorphic
Mica Schist
Mica Schist (primarily Muscovite or Biotite sheet silicates)
Hardness: 2-2.5 (mica layers) to 6-7 (if quartz rich); Color: Silvery-gray, golden-brown, or bronze; Luster: Pearly to metallic; Structure: Schistose foliation with visible aligned mineral flakes; Cleavage: Perfect basal cleavage in individual mica crystals.
- Hardness
- 2-2
- Color
- Silvery-gray, golden-brown, or bronze
- Luster
- Pearly to metallic
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Physical properties
Hardness: 2-2.5 (mica layers) to 6-7 (if quartz rich); Color: Silvery-gray, golden-brown, or bronze; Luster: Pearly to metallic; Structure: Schistose foliation with visible aligned mineral flakes; Cleavage: Perfect basal cleavage in individual mica crystals.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high heat and pressure. This process causes clay minerals to recrystallize into large, visible mica flakes aligned perpendicular to the direction of pressure.
Uses & applications
Historically used for hearth stones and dimension stone in walls; today used primarily as a source of ground mica for lubricants, wallpaper glitter, joint compound, and electrical insulation.
Geological facts
The word 'schist' is derived from the Greek word 'schistos,' meaning 'split,' referring to the ease with which these rocks can be flaked along the planes of the mica flakes. It often contains 'porphyroblasts' like garnets.
Field identification & locations
Identify in the field by its distinct 'sparkle' or 'sheen' in sunlight and its tendency to flake off in thin, glittery scales when scratched. It is commonly found in mountain belts and Precambrian shield areas.
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