Tanzanite, the birthstone for December, was discovered in 1967 anf by the late 1980’s and 1990’s its popularity had already taken the world by storm. A robust gem its hardness is measured 6.5 on the Moh's scale. The Tanzanites are found in sausage shaped pockets of schist, sometimes at great depths. Most Tanzanite gems are found in irregular crystal shapes and are a dark brownish color.