A variety of the mineral zoisite, tanzanite was discovered in Tanzania in 1967. Tiffany & Co launched it onto the commercial gemstone market with the name tanzanite to reflect its geographical origins (rather more poetic than 'blue zoisite' or the chemical name of calcium aluminum silicate) with the tag line: "tanzanite can now only be found in significant quantities in only two places in the world. In Tanzania. And Tiffany's".
Tanzanite is found in an area of extensive tectonic activity, and is thought to have formed over 585 million years ago (young compared to the worlds oldest gemstones, Zircons, some of which have been dated to 4.4 billion years ago). It grows in orthorhombic crystals, which are often found broken due to its brittle nature.
A tanzanite faceted gem, or crystal may be seen to exhibit two or three different colours when viewed from different directions, sometimes even with the naked eye or with a gemmological tool called a dicroscope. This is due to pleochroism where light rays are absorbed differently in as they vibrate in different directions through the stone. In a natural and unheated tanzanite it may be possible to see three colours in one stone, but not all in the same direction. This includes a blue, a greenish yellow-brown and the desirable violet. Many tanzanites are heat treated to remove the yellowish brown colouration, leaving the commercially desirable violet and deep blue.
Gemstone care is very important with this stone as it not not as durable as stones such as diamonds, sapphires and rubies. With a hardness of 6.5 on the Mohs hardness scale it prone to damage and to scratches. It is also brittle; protect this stone from extremes of temperature as it is susceptible to thermal shock, and do not clean in ultrasonic jewellery cleaners. This lower durability means it should be set in jewellery that protects the gemstone, such earrings or pendants, or in rings that are for occasional use only.
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