Metamorphic
Schist
Mica Schist (Medium-grade Metamorphic Rock)
Hardness: 3.5 - 4 (Mohs); Color: Silvery-grey to graphite-grey; Luster: Pearly to sub-metallic; Crystal Structure: Foliated; Cleavage: Perfect basal cleavage on individual mica flakes; Specific Gravity: 2.7 - 2.8
- Hardness
- 3
- Color
- Silvery-grey to graphite-grey
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5 - 4 (Mohs); Color: Silvery-grey to graphite-grey; Luster: Pearly to sub-metallic; Crystal Structure: Foliated; Cleavage: Perfect basal cleavage on individual mica flakes; Specific Gravity: 2.7 - 2.8
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate pressure and temperature conditions. It typically dates back to tectonic mountain-building events (often Paleozoic or Proterozoic).
Uses & applications
Used as decorative stone in architecture, landscape pavers, and historically as a roofing material. Due to its flaky nature, it is less common in heavy industrial load-bearing construction.
Geological facts
The word 'schist' is derived from the Greek word 'schízein', meaning 'to split,' referring to how easily the rock breaks along its foliated planes. It is a key indicator rock used by geologists to determine the metamorphic history of a region.
Field identification & locations
Identify by its 'schistosity'—a platy, layered appearance with visible mica flakes that glitter in the sun. Commonly found in Appalachian Mountains (USA), the Alps, and the Scottish Highlands. Collectors look for garnet inclusions common in this type of rock.
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