Tanzanite is the blue to violet to purple variety of the mineral zoisite. It is mined commercially only in one area of the world: the Merelani Hills of Tanzania, which is where it gets its name.
Tanzanite’s appearance is influenced greatly by its pleochroism, which is the ability of a gemstone to show different colors when viewed in different crystal directions. Tanzanite can be violetish blue—similar to a sapphire color—or much more purplish. Often, both the violetish blue and purplish colors are readily visible in a fashioned stone when it is gently rocked and tilted.