metamorphic
Mica Schist fragment
Mica Schist (KAl2(AlSi3O10)(OH)2 / K(Mg,Fe)3(AlSi3O10)(OH)2)
Hardness: 2-2.5 on Mohs scale; Color: Dark grey to silvery black; Luster: Vitreous to pearly (shimmery); Crystal Structure: Monoclinic; Cleavage: Perfect basal; Specific Gravity: 2.7–3.3
- Hardness
- 2-2
- Color
- Dark grey to silvery black
- Luster
- Vitreous to pearly (shimmery)
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Physical properties
Hardness: 2-2.5 on Mohs scale; Color: Dark grey to silvery black; Luster: Vitreous to pearly (shimmery); Crystal Structure: Monoclinic; Cleavage: Perfect basal; Specific Gravity: 2.7–3.3
Formation & geological history
Formed by the regional metamorphism of clay-rich sedimentary rocks (shales) or igneous rocks under medium-grade temperatures and pressures. This process causes micas to align, creating a foliated texture.
Uses & applications
Schist is used as a decorative stone in garden walls and flagstone. Micas extracted from it are used in the electronics industry as insulators, in cosmetics for shimmer, and in joint compounds.
Geological facts
The term 'schist' comes from the Greek word 'schistos', meaning 'split', referring to the ease with which these rocks can be divided into thin layers. Large mica sheets are known as 'books'.
Field identification & locations
Identified in the field by its distinct foliation (schistosity) and high shimmer or glitter effect when turned in the light. Often found in mountainous regions or ancient crystalline shield areas.
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