Tanzanite is really a blue variety of "zoisite." Zoisite was commonly known for its pink variety, thulite (a massive ornamental pink stone), until 1966 when a new gem was discovered near Mount Kilimanjaro in northern Tanzania. It was a deep blue gemstone thought to be a sapphire until chemical analysis proved it to be a new variety of zoisite. Tanzanite crystals are transparent and the color ranges from sapphire blue to amethyst violet. Some tanzanite is heat treated to remove yellow or brown tinges and to enhance the blue color. Tanzanite is 6½ to 7 on the Mohs hardness scale and is a delicate stone. All tanzanite is irradiated to obtain the indigo blue color, and then heat treated to improve and strengthen the color. The treatments do not affect the durability of the gemstone so there should be no concern when this enhancement is disclosed. Tanzanite is the stone for the twenty-forth anniversary.