Tanzanite, a variety of the mineral zoisite, is a blue to blue-violet gemstone, frequently used in jewelry, that was popularized by Tiffany & Co after its discovery in the late 60s.
With a hardness of 6 to 6.5 on Mohs scale, tanzanite is rather soft for a gemstone, which limits its use in jewelry, as it is prone to wear and scratching. The saturation (and sometimes the nuance) of its color changes based on the angle at which it is viewed. Many of the tanzanite gemstones available on the market have been heat-treated to enhance their color, which also affects tanzanite's price - natural deep blue tanzanites are very rare and highly appreciated.
Tanzanite's value also depends on its color, among other factors - blue gemstones with slight violet nuances are typically higher in value than purely violet specimens. Another property that affects tanzanite's price is its color change, based on the source of light, as well as its pleochroism, i.e. the fact that the color of a given gemstone changes based on the angle at which it is viewed.
Tanzanite can be found only in the Merelani Hills area in Tanzania; no other deposits of tanzanite have been found to date.
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