metamorphic
Schist (Kyanite Schist)
Kyanite-Mica Schist (primarily Al2SiO5, KAl2(AlSi3O10)(OH)2, and SiO2)
Hardness: 5.5-7 (variable); Color: Silvery-gray, blue, or greenish; Luster: Pearly to sub-metallic; Structure: Foliated with visible elongated lath-like crystals; Cleavage: One perfect direction in mica and kyanite components.
- Hardness
- 5
- Color
- Silvery-gray, blue, or greenish
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 5.5-7 (variable); Color: Silvery-gray, blue, or greenish; Luster: Pearly to sub-metallic; Structure: Foliated with visible elongated lath-like crystals; Cleavage: One perfect direction in mica and kyanite components.
Formation & geological history
Formed from the regional metamorphism of clay-rich sedimentary rocks (pelites) under high pressure and medium-to-high temperature conditions during mountain-building events (orogenies).
Uses & applications
Used primarily as decorative stone, in construction as flagstone or dimension stone, and as a source for kyanite which is used in high-temperature ceramics and abrasives.
Geological facts
The presence of kyanite indicates the rock was subjected to pressures greater than 4 kilobars, equivalent to a depth of over 15 kilometers. It is a classic 'index mineral' for metamorphic grade.
Field identification & locations
Identify by its sparkly, foliated 'schistose' texture and the presence of elongated, blade-like crystals. Common in core areas of eroded mountain ranges like the Appalachians or Alps. Look for 'sheen' from mica.
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