metamorphic
Schist
Mica Schist (primarily Muscovite and Quartz)
Hardness: 3.5–4.0; Color: Silvery-gray, tan, or metallic; Luster: Pearly to sub-metallic due to mica; Structure: Schistose foliation with visible medium-to-coarse grained minerals; Cleavage: Perfect basal cleavage in individual mica flakes.
- Hardness
- 3
- Color
- Silvery-gray, tan, or metallic
- Luster
- Pearly to sub-metallic due to mica
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Physical properties
Hardness: 3.5–4.0; Color: Silvery-gray, tan, or metallic; Luster: Pearly to sub-metallic due to mica; Structure: Schistose foliation with visible medium-to-coarse grained minerals; Cleavage: Perfect basal cleavage in individual mica flakes.
Formation & geological history
Formed through regional metamorphism of shale or mudstone at medium grades of pressure and temperature (300-450 degrees Celsius). During this process, platy minerals like mica align perpendicular to the direction of pressure, creating the characteristic layered appearance.
Uses & applications
Commonly used as a decorative building stone for walls, flagstones, and paving. Historically used for roofing slates in some regions. High-quality specimens are collected for geological studies.
Geological facts
The word 'schist' is derived from the Greek 'schistos,' meaning 'easy to split.' It is a key indicator of plate tectonic activity where mountain-building events (orogeny) have occurred in the geological past.
Field identification & locations
Identify in the field by its 'schistosity'—a sparkly, layered appearance that easily flakes when scratched. It is commonly found in metamorphic terranes such as the Appalachian Mountains, the Scottish Highlands, or the Himalayas. Collectors should look for garnets that often grow as distinct crystals within the schist matrix.
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