Tanzanite 1 

Tanzanite is an extremely rare gemstone that was first discovered in Northern Tanzania in 1967.  A variety of the mineral zoisite, it's usually reddish brown when mined and needs to be heat treated in order for it to change colour.  The area where it's mined is just four square kilometres and there's only a limited amount of material left to be mined.   Due to its rarity, it's expensive and tends to be faceted for use in ladies jewellery.  Found on the foothills of Mount Kilimanjaro, its scientific name is blue zoisite however it was re named by the President and Chairman of the American jeweller Tiffany & Co, shortly before being presented to the world in 1968.

Further Reading:
Tanzanite by Geology.com
The Tanzanite Foundation