metamorphic
Mica Schist
Mica Schist (predominantly Muscovite/Biotite)
Hardness: 3.5-4 (varies with composition); Color: silvery-gray to brownish-gold due to weathering; Luster: Pearly to sub-metallic; Crystal structure: Foliated (schistosity) with visible plate-like grains; Specific Gravity: 2.7-2.8
- Hardness
- 3
- Color
- silvery-gray to brownish-gold due to weathering
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4 (varies with composition); Color: silvery-gray to brownish-gold due to weathering; Luster: Pearly to sub-metallic; Crystal structure: Foliated (schistosity) with visible plate-like grains; Specific Gravity: 2.7-2.8
Formation & geological history
Formed through medium-grade regional metamorphism of clay-rich sedimentary rocks (shale or mudstone). Subjected to high heat and pressure, typically during mountain building events (orogeny). Age varies by location, often associated with Precambrian or Paleozoic eras.
Uses & applications
Used historically as a building stone or decorative facade. Finely ground mica is used as a lubricant, in electronics, and in the paint and cosmetics industry for its shimmer. Collectors value it for aesthetic leafy texture.
Geological facts
Mica schist is famous for its 'schistosity,' a texture where mica grains grow large enough to be seen with the naked eye and align in parallel layers, causing the rock to split easily into thin plates. It represents a middle step in metamorphism between phyllite and gneiss.
Field identification & locations
Identify in the field by its distinct glittering, flaky appearance and layers that can often be picked apart with a fingernail or knife. Common in mountain ranges such as the Appalachians or the Alps. Look for garnets, which frequently grow inside schist as 'accessory minerals.'
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