Kyanite is a polymorph of aluminum silicate. There are two other minerals with the same composition, andalusite and sillimanite. Which mineral is formed is dependent on the temperature and pressure at the time of formation; kyanite is usually formed at the highest temperatures and pressures.
Appearance
The name kyanite originates from the Greek word kyanos, which means "blue." It can be found in a striking blue color, but also can be gray, white or green, and very rarely, black. It has the singular characteristic of combining varying hardnesses in the same crystal. Scratched one way it has a hardness of 4.5, and at 90 degrees from this it has a hardness of 6.5.
History
Some of the earliest specimens of kyanite were found in Switzerland, and initially it was thought to be sapphire, after a mistake was made by the French mineralogist Saussure. Early in its history kyanite was recognized for its high temperature stability and was sought for the manufacture of spark plugs and as refractories used to line furnaces at the beginning of WW1.
Largest Source
The world's largest producer of kyanite by far is the US. It can be found in a number of states including California, Georgia, Nevada, Virginia, and North and South Carolina. US production of kyanite is more than that of the rest of the world combined.
International Sources of Kyanite
After the US, there are a number of significant producers of kyanite around the world. India, Brazil, China, and Australia are the main other sources, but minor amounts are to be found in many other countries, although usually in the other mineral form of andalusite.
Non-industrial Uses
Although kyanite is mostly used for industrial purposes, it also can produce some very nice jewelry when found in its blue form. The New Age movement puts particular importance on kyanite as having calming effects.
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