mineral
Blue-gray kyanite crystal
Kyanite, Al₂SiO₅
AI-generated identification · may be incorrectBlue-gray, bladed crystal with vitreous to pearly luster and prominent lengthwise cleavage. Mohs hardness varies by direction: about 4.5–5 parallel to the blades and 6.5–7 across them; triclinic crystal structure, specific gravity about 3.5–3.7.
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Physical properties
Blue-gray, bladed crystal with vitreous to pearly luster and prominent lengthwise cleavage. Mohs hardness varies by direction: about 4.5–5 parallel to the blades and 6.5–7 across them; triclinic crystal structure, specific gravity about 3.5–3.7.
Formation & geological history
Forms mainly during regional metamorphism of aluminum-rich sediments, commonly in schist and gneiss; crystals occur in rocks of many geological ages.
Uses & applications
Used as a high-temperature ceramic and refractory material; attractive specimens are collected and occasionally cut as gemstones.
Geological facts
Kyanite’s strongly direction-dependent hardness is unusual and helps distinguish it from similar blue minerals.
Field identification & locations
Look for flat, bladed blue crystals, often with lengthwise striations, in metamorphic rocks. Notable sources include Nepal, Brazil, India, and the United States; small rough specimens commonly sell for about $5–$30, depending on quality and size.
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