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Article: Is Unheated Tanzanite More Valuable?

Is Unheated Tanzanite More Valuable?

Is Unheated Tanzanite More Valuable?

Be wary of retailers claiming a price premium for “unheated” tanzanite. All tanzanite must be heated to reveal its distinctive blue color. A very small percentage of stones are naturally blue from underground heating, while the majority are gently heated after mining to remove brown veils that obscure the blue.

Below: Freshly mined tanzanite: some is blue, some is brown.

It’s a common misconception that longer or more intense heating makes tanzanite bluer. In reality, the blue color is determined by the vanadium content present when the stone formed and can't be changed by heating it up: otherwise sellers would just heat all the rough until it was the top shade! All heating does is remove brown-toned shades that veil the blue, without enhancing or altering the blue itself.

Many buyers are enticed by the idea of extra-rare “unheated” tanzanite. However, there is currently no scientific method to verify whether a stone was heated naturally or artificially, so claims of “unheated” tanzanite cannot be substantiated. The GIA (Gemological Institute of America) and all other leading laboratories will not certify whether a tanzanite has been heated. As of 2024, the prestigious Gübelin Lab in Switzerland can certify some stones as unheated, but this technique has not been adopted by other leading labs.

It’s also important to distinguish tanzanite heating from the “heat treatment” used in sapphires and rubies, which involves high temperatures over days and can change chemical structure and value. Tanzanite’s gentle heating is normal, permanent, and accepted worldwide—it does not affect the stone’s value.

Pricing for tanzanite is based on color, clarity, cut, and size, not on whether it has been heated.

Buyer beware: Claims of “unheated tanzanite” are misleading and should not influence price.

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