What is Tanzanite?
At its breathtaking best, tanzanite looks the spitting image of Kashmir sapphire – exhibiting the rich, royal velvety blue those stones are prized for. But costing a fraction of the price. Then the merest hint of violet creeps in and tips off experts that the stone is something else.
That “something else” is a blue zoisite, rechristened tanzanite by Tiffany in 1969 to honor its one source, Tanzania, and considered by many the pride of that gem-rich East African country.
As retailers and jewelry manufacturers became the primary users of tanzanite, size preferences dropped decidedly below 10 carats into the 1-to 6 carat- range. At the same time, the gem has begun to be appreciated far more on its own terms and far less as a sapphire substitute.
This isn’t to say that the old connoisseur color ideal for this gem, a Kashmir blue, was abandoned. But there is greater admiration for tanzanites that don’t ape fine sapphires, a factor slowly freeing the gem from its second-class status as a sapphire substitute.
It is going too far to say that Kashmir-blue and strong violetish-blue tanzanites are equals. The Kashmir color is finer. The violetish stones are attractive and need no apologies. More important, the economics of cutting will always dictate a preponderance of these stones.
Tanzanite is a trichroic stone. This means that it gives of different colors when viewed from different directions or axes. In tanzanite, one axis is blue, and another violetish and the last reddish brown or bronze. When shown, tanzanite rough, cutters look for strong trichroism, plus, of course, intense colors, as desirable signs. after cutting, the stone is heated to induce a permanent color change – usually from a brownish to bluish color. The stones with the strongest reddish brown in them before heating bake to the deepest blue. In any case, without heating, tanzanite would be unmarketable.
“The Kashmir-blue color is an ideal that can more readily be realized with tanzanite today than sapphire.” Miller says “It’s a shame to see so many stones deprived of the chance to embody that ideal.”
Stones that embody the Kashmir ideal have been known to fool jewelers – sometimes with dire consequences. Jewelry bench men with no gemological training who have mistraken tanzanite for sapphire have frequently destroyed stones. The reason: Tanzanite, a softer and more fragile gem than sapphire, cracks, even shatters, when exposed to extreme temperatures or sudden temperature changes.