description Kyanite Overview
Kyanite is an aluminosilicate mineral with the chemical formula Al2SiO5. It is distinguished by strong directional variation in hardness: its hardness differs depending on whether a specimen is tested parallel or perpendicular to its crystal structure. Kyanite commonly occurs in blue, although other colors are known, and transparent blue material can be cut as a gemstone. The mineral is also used as an industrial source of alumina and silica.
help Kyanite FAQ
What is the chemical formula of kyanite?
Kyanite is an aluminosilicate mineral with the chemical formula Al2SiO5. The same formula is shared by related polymorphs such as andalusite and sillimanite.
Why does kyanite have different hardness values?
Kyanite has strong directional variation in hardness because its crystal structure responds differently to testing in different directions. It is softer when tested parallel to one crystallographic direction and harder when tested perpendicular to it.
What color is kyanite usually?
Kyanite is commonly blue, although specimens can show other colors and color zoning. The blue color is one reason transparent specimens are sometimes cut as gemstones.
Is kyanite used as a gemstone?
Yes. Clear blue kyanite can be cut and polished as a gemstone, although much kyanite is collected or used as a mineral specimen. Its directional hardness makes cutting and shaping more demanding than for many common gems.
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