metamorphic
Schist
Mica Schist
Hardness: 3.5-4; Color: Silvery-gray, greenish-gray, or bluish; Luster: Pearly to sub-metallic; Crystal Structure: Foliated (schistosity); Cleavage: Excellent in one direction due to mica content; Specific Gravity: 2.7-2.9.
- Hardness
- 3
- Color
- Silvery-gray, greenish-gray, or bluish
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4; Color: Silvery-gray, greenish-gray, or bluish; Luster: Pearly to sub-metallic; Crystal Structure: Foliated (schistosity); Cleavage: Excellent in one direction due to mica content; Specific Gravity: 2.7-2.9.
Formation & geological history
Formed from the metamorphism of shale or mudstone under intermediate to high temperatures and pressures. This creates a rock with visible mineral grains that are platy or elongated. Usually associated with regional metamorphism in orogenic (mountain-building) belts.
Uses & applications
Used as a decorative stone in architecture, for garden walls, flagstones, and occasionally for roofing. Rarely holds significant industrial use due to its tendency to flake, but mica extracted from it is used in electronics and cosmetics.
Geological facts
The term schist comes from the Greek word 'schizein', meaning 'to split', referring to the ease with which the rock can be cleaved along the planes of its plate-like minerals. Some schists contain garnet or staurolite crystals embedded within the mica layers.
Field identification & locations
Identify in the field by its distinct layered (foliated) appearance and its tendency to sparkle or glitter in the sun due to the abundance of mica flakes. It feels slightly 'greasy' or slippery when rubbed if it contains high chlorite or talc. Found commonly in mountain ranges like the Appalachians, Alps, or Himalayas.
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