metamorphic
Schist
Mica Schist (variety: Muscovite/Biotite Schist)
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray, greenish, or golden-tan with a metallic sheen; Luster: Pearly to sub-metallic; Crystal structure: Foliated (schistosity) with medium to large grains; Cleavage: Excellent in the mica layers, allowing it to split into thin sheets; Specific gravity: 2.7–2.8.
- Hardness
- 3
- Color
- Silvery-gray, greenish, or golden-tan with a metallic sheen
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray, greenish, or golden-tan with a metallic sheen; Luster: Pearly to sub-metallic; Crystal structure: Foliated (schistosity) with medium to large grains; Cleavage: Excellent in the mica layers, allowing it to split into thin sheets; Specific gravity: 2.7–2.8.
Formation & geological history
Formed by regional metamorphism of shale or mudstone under high pressure and temperature (intermediate grade). The mica minerals grow in parallel alignment perpendicular to the direction of pressure. Age ranges from Precambrian to Cenozoic depending on the tectonic belt.
Uses & applications
Primary use is decorative, such as garden stones, wall cladding, and paving. Historically used for roofing slates or writing tablets. Some high-quality specimens are used in the production of grounding materials or in jewelry if it contains garnets.
Geological facts
The word 'schist' is derived from the Greek word 'schizein', which means 'to split'. Schist is unique because it contains over 50% platy and elongated minerals like mica, which gives it its characteristic 'sparkle' under sunlight.
Field identification & locations
Identify in the field by its distinct foliation (layering) and its tendency to flake off into plate-like minerals when scratched. Look for 'schistosity'—a shimmering, glittery surface. Common in mountain ranges like the Appalachians, Alps, or Himalayas.
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