Quick answer: not imminently, but it is genuinely finite. All gem tanzanite comes from a mining zone roughly 7 km long and 2 km wide in the Mererani Hills of northern Tanzania. A 2018 estimate put remaining reserves around 109 million carats, mostly in one mining block (Wikipedia, citing a 2018 report). Production is not collapsing; recorded output actually jumped after Tanzania walled off the mines. But there is no second source anywhere on Earth, so “rarer than diamond” is a fair description, and “running out in a decade” is marketing.
One hillside, one gem
Tanzanite is the blue-violet variety of the mineral zoisite. It needs an unusual recipe: a trace of vanadium, specific metamorphic rocks, and a particular heat-and-pressure history, all of which came together at Mererani. We covered the geology in Tanzanite: the gemstone that only exists in a few square miles on Earth. This post is about supply.
Who actually found it
The popular story credits Manuel de Souza, a Goan tailor and part-time prospector, in July 1967. But the Tanzanian government recognizes Jumanne Mhero Ngoma, who came across blue stones in the Mererani hills that January. The name “tanzanite” came from Tiffany & Co. vice president Henry B. Platt, who felt “blue zoisite” wouldn’t sell. Tiffany launched it in 1968 with the line “in Tanzania and at Tiffany’s” (Wikipedia).
The 24 km wall
Smuggling was so widespread that Tanzania built a 24 km perimeter wall around the mining area. Recorded production went from 147.7 kg in 2018 to a record 781.2 kg in 2019 (Wikipedia). The stones were always coming out of the ground; the wall changed how many were counted.
The miner who became a millionaire overnight
In June 2020, small-scale miner Saniniu Laizer found two rough tanzanites weighing a combined 11.14 kg (about 55,700 carats). The Tanzanian government bought them for about US$3.35 million (around Sh7.7 billion), beating the previous record of a 3.38 kg stone from 2005 (Wikipedia; The Citizen). Laizer said he planned to build a school and a shopping mall near his home.
How the mines are divided
In 1990 the government split Mererani into Blocks A through D. Blocks A and C went to larger operators; B and D were reserved for local small-scale miners (Wikipedia). Block C holds the largest share of the estimated reserve, which is why corporate changes there move the whole market.
Almost all tanzanite is heated, and that’s normal
Most rough comes out brownish. Gentle heating, typically around 370-390 °C for about 30 minutes, removes the brown and leaves the blue-violet. Untreated crystals are trichroic, showing three colors depending on direction; heated stones become dichroic, mainly blue and violet (Wikipedia). It’s a stable, accepted treatment, and the trade assumes it. See Pleochroism.
A birthstone first
In 2002 the American Gem Trade Association added tanzanite as a December birthstone, the first change to the official list since 1912 (Wikipedia). See Birthstones, decoded.
FAQ
Will tanzanite go up in value? Nobody can promise that. Prices depend on mining output, marketing, and demand, not just reserves.
Is rough tanzanite worth collecting? Rough and micro specimens are the most affordable way to own material from the only locality on Earth, and natural crystal shapes show the trichroism that cut stones lose.
Related pieces in the shop
Sources: Wikipedia, Tanzanite (incl. 2018 reserve report and production figures); The Citizen (Tanzania), June 2020.
