Silicate mineral, one of several phases in the aluminum silicate (Al2SiO5) system. Its colour ranges from gray-green to black or blue, with blue and blue-gray being most common. It occurs in Switzerland, Italy, the Ural Mountains, and New England (U.S.). Kyanite is a raw material in the manufacture of spark plugs. A clear, deep-blue variety is sometimes cut as a gemstone.
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