Tanzanite gemstone is a blue variety of Zoisite. Found in only one area of the world- the foothills of Kilimanjaro. Very few stones are actually found in the desired violetish blue colour, most has far too much yellow and brown in them and must be heated before it can be used for jewellery. Some say that's how all blue coloured Tanzanites came to be but there is a difference. Stones that come originally blue from the ground are trichroic while the heated ones are dichroic. That doesn't make them less beautiful or physically worse but as with other gemstones, untreated Tanzanites command premiums. Tanzanite is relatively brittle, so it is better to use it in earrings and necklaces, rather than rings, where it can be damaged more easily. The most desired hue of Tanzanite is violetish blue, vivid tone without any grey or brown mask.