Tanzanite is a rare gem. It is found mostly in the foothills of Mount Kilimanjaro (Tanzania). It has a deep purplish blue colour which is unique to tanzanite only.
The Gemmological Institute of America classifies tanzanite as a Type I gemstone, meaning it is normally eye-flawless. Gems with eye-visible inclusions will be traded at deep discounts. Tanzanite in its rough state is usually a reddish brown colour. It requires artificial heat treatment to 600°C in a gemmological oven to bring out the blue-violet of the stone. Since heat treatment is universal, it has no effect on price, and finished gems are assumed to be heat treated.
At 6.5 on the Moh’s scale of Hardness, tanzanite is not recommended for everyday wear unless well protected in its setting.