metamorphic
Schist
Mica Schist
Hardness: 3.5-4; Color: Silvery-gray, greenish, or brown; Luster: Pearly to sub-metallic (shimmering); Crystal structure: Foliated (platey minerals aligned); Cleavage: Perfect in one direction along mica grains; Specific Gravity: 2.7–2.8.
- Hardness
- 3
- Color
- Silvery-gray, greenish, or brown
- Luster
- Pearly to sub-metallic (shimmering)
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Physical properties
Hardness: 3.5-4; Color: Silvery-gray, greenish, or brown; Luster: Pearly to sub-metallic (shimmering); Crystal structure: Foliated (platey minerals aligned); Cleavage: Perfect in one direction along mica grains; Specific Gravity: 2.7–2.8.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone at medium grades of temperature and pressure. It originates from deep burial and tectonic activity, often during mountain-building events.
Uses & applications
Historically used for flagstone, roofing, and wall construction. Some varieties containing garnet or graphite are mined for those specific minerals; generally has low industrial value but high aesthetic value in landscaping.
Geological facts
The word 'schist' is derived from the Greek word 'schizein', meaning 'to split', referring to the ease with which it can be split along the plane of its platy minerals. It is one of the most common metamorphic rocks in the Earth's crust.
Field identification & locations
Identify in the field by its characteristic 'schistosity' or shimmer caused by aligned mica flakes. Look for wavy or crinkled mineral layers. Commonly found in mountainous regions like the Appalachians, Alps, or Himalayas.
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