While the mineral zoisite has been known for some time, gem-quality zoisite, called Tanzanite, wasn't found until 1967, when a deposit was uncovered in Tanzania. This is still the only source for tanzanite, one of the most recent additions to the gem world. Tanzanite gained almost immediate popularity both for its scarcity and its rich, blue-violet color. It is often heat-treated to bring out a uniform color. Tanzanite is noted for its trichroism, an optical phenomenon - appearing three colors (blue, violet and burgundy/brown) depending on each stone's crystal orientation. Tanzanite may also change appearance when viewed under alternate lighting.
Tanzanite is rated 6.5 on the Mohs scale of hardness. While a prized stone, caution should be used when it is worn in rings, since it is fairly soft and can be scratched or chipped. Although it usually has good clarity, tanzanite can be damaged by ultrasonic cleaners, so other cleaning methods are recommended.