metamorphic
Schist
Mica Schist (Medium-grade metamorphic rock)
Hardness: 3.5–4.5 (Mohs); Color: Silvery-gray, brownish, or dark green with glittery flakes; Luster: Pearly to sub-metallic; Crystal structure: Foliated (Schistosity); Cleavage: Excellent in one direction for individual mica minerals; Specific gravity: 2.7–2.8
- Hardness
- 3
- Color
- Silvery-gray, brownish, or dark green with glittery flakes
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5–4.5 (Mohs); Color: Silvery-gray, brownish, or dark green with glittery flakes; Luster: Pearly to sub-metallic; Crystal structure: Foliated (Schistosity); Cleavage: Excellent in one direction for individual mica minerals; Specific gravity: 2.7–2.8
Formation & geological history
Formed from the metamorphosis of shale, mudstone, or siltstone under medium-grade temperature and pressure conditions (typically 400-500 degrees Celsius). The visible mica crystals grow perpendicular to the direction of pressure.
Uses & applications
Historically used for flagstone, roofing tiles, and decorative garden paths. In modern times, it is occasionally used as a filler in building materials or as a source of mica for electrical insulation and cosmetics.
Geological facts
The word 'schist' is derived from the Greek word 'schistos,' meaning 'to split,' referring to how easily the rock can peel into thin slabs. Manhattan, NYC, is famously built upon Manhattan Schist, which provides a solid foundation for skyscrapers.
Field identification & locations
Identify in the field by looking for a 'glittery' or 'shiny' appearance due to large mica flakes and a distinct layered (foliated) texture. It scales easily with a hammer. Common in mountain ranges like the Appalachians, Alps, and Himalayas.
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