Tanzanite is a relatively recent addition to the gem world. It was originally marketed as a sapphire substitute, but people fell in love with the gem and it gained a life all it's own. Today, value is based not on how blue or purple the color is, but how intense it's color is. Tanzanite is produced only in Tanzania, and usually comes out of the ground brown. Heat treatment changes the brown to blue, but can not add color intensity to the stone that is not already present. The price of tanzanite has fluctuated wildly over the last decade, but since most tanzanite is now under the marketing arm of the Tanzanite Foundation, pricing has stabilized. The hardness of tanzanite is 7, making it suitable for most jewelry other than everyday rings.
Treatments: Heating to change color.