Tanzanite is the most famous zoisite. It is a transparent blue zoisite that is colored by the presence of vanadium. Some blue zoisite is found naturally, but most is produced by heat-treating brown zoisite. The heat changes the oxidation state of vanadium to produce the blue color. Tanzanite is the second most popular blue stone, after sapphire. It is a rare gem only found in one small area in northern Tanzania.