The following free information is from the website: http://en.wikipedia.org/wiki/Tanzanite
Tanzanite is the blue/purple variety of the mineralzoisite which was discovered in the Meralani (Merelani) Hills of Northern Tanzania in 1967, near the city of Arusha. It is used as a gemstone. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet, and burgundy depending on crystal orientation.
Tanzanite in its rough state is usually a reddish brown color. It requires artificial heat treatment to 600 °C in a gemological oven to bring out the blue violet of the stone.[citation needed] Tanzanite is a rare gem.[1][2] It is found mostly in the foothills of Mount Kilimanjaro. The mineral is named after Tanzania, the country where it was first discovered.
Tanzanite is the blue/purple variety of the mineralzoisite which was discovered in the Meralani (Merelani) Hills of Northern Tanzania in 1967, near the city of Arusha. It is used as a gemstone. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet, and burgundy depending on crystal orientation.
Tanzanite in its rough state is usually a reddish brown color. It requires artificial heat treatment to 600 °C in a gemological oven to bring out the blue violet of the stone.[citation needed] Tanzanite is a rare gem.[1][2] It is found mostly in the foothills of Mount Kilimanjaro. The mineral is named after Tanzania, the country where it was first discovered.
The hardness (Mohs scale) : 6.5
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It is o.k. and acceptable , if the sellers do not tell the buyers that the stones are heat treated as it is widely known that to get the good color tanzanite, the stones have to be heat treated.
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