Probably 99.99 percent of tanzanite (blue zoisite) is heated to get the gemstone's characteristic saturated purple-blue color. In fact, most dealers will tell you it's not tanzanite until it's heated to create that color. But though rare, there are natural purple-blue tanzanites. NATURAL COLOR To acquire natural-color tanzanite, you must buy rough, says Dana Schorr, tanzanite specialist and owner of Schorr Marketing and Sales in Santa Barbara, Calif. "You buy parcels of rough, because people generally don't treat the rough." Heating rough can extend fractures or cause inclusions to explode, both of which result in more waste and smaller stones. "You want to trim off all of the cracks and inclusions that may cause problems later," Schorr advises. If you do find natural-color tanzanite, the stones typically will be large. "Especially in larger stones, there's a lot of rough that you