Is Unheated Tanzanite More Valuable?

Be cautious of retailers promoting a price premium for “unheated” tanzanite.

All tanzanite is heated to reveal its signature blue color. A very small percentage is naturally heated underground, while most is gently heated after mining to remove brown tones that veil the blue.

It’s a common misconception that heating makes tanzanite bluer. In reality, the color is determined by the vanadium content when the stone forms—heating cannot enhance or deepen it. Heating simply removes unwanted brown hues or veil than forms when tanzanite crystals form. 

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

Unheated tanzanite often shows a mix of brown, green, violet, and blue tones, rather than the clean, vibrant blue most people expect.

Importantly, there is currently no reliable way to prove whether a stone was heated naturally or artificially. The GIA and other leading laboratories do not certify “unheated” tanzanite, and such claims cannot be substantiated.

Unlike sapphires and rubies, where high-temperature treatment can alter value, tanzanite’s gentle heating is standard, permanent, and fully accepted worldwide.

Question : I heard the Gübelin Gem Lab can prove if tanzanite is heated or not - is this true ? 

Short answer: not in the way people think. The Gübelin Gem Lab has explored methods to identify unheated tanzanite in some cases. However, this is not widely standardised or consistently applied across the industry. More importantly: There is no universally accepted scientific method to reliably distinguish natural vs. post-mining heating in tanzanite.

 Because of this, GIA and other leading labs do not certify tanzanite as “unheated.” What this means in practice: Gübelin may issue opinions in limited cases, using advanced research techniques But this is not a broadly recognised, consistent certification standard And it is not something most stones can receive Bottom line (industry reality): Even with Gübelin’s work, “unheated tanzanite” is still not reliably certifiable at scale, and claims should be treated cautiously.

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.