metamorphic
Kyanite (in Schist Matrix)
Kyanite (Al2SiO5)
Hardness: Anisotropic (4.5 to 5 along the long axis and 6.5 to 7 across it); Color: Bluish-gray to black in this specimen; Luster: Vitreous to pearly; Crystal structure: Triclinic (typically bladed); Cleavage: Perfect in one direction.
- Hardness
- Anisotropic (4
- Color
- Bluish-gray to black in this specimen
- Luster
- Vitreous to pearly
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Physical properties
Hardness: Anisotropic (4.5 to 5 along the long axis and 6.5 to 7 across it); Color: Bluish-gray to black in this specimen; Luster: Vitreous to pearly; Crystal structure: Triclinic (typically bladed); Cleavage: Perfect in one direction.
Formation & geological history
Formed through high-pressure regional metamorphism of clay-rich sedimentary rocks (pelites). It is typically found in gneiss or schist and serves as an index mineral for high-grade metamorphic conditions.
Uses & applications
Used industrially for manufacturing refractory products like porcelain, kiln linings, and spark plugs due to its high heat resistance. Translucent blue varieties are used as gemstones and for metaphysical collecting.
Geological facts
Kyanite is unique because its hardness varies significantly depending on the direction it is scratched. It is a polymorph with Andalusite and Sillimanite, meaning they share the same chemistry but have different structures based on pressure and temperature.
Field identification & locations
Identify by its bladed crystal form and characteristic blue or gray tint. This specific specimen appears to be raw kyanite embedded in a mica-schist matrix. Common locations include Brazil, India, and parts of the Appalachian Mountains in the USA.
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