Tanzania — verified dealers & sourcing guide

Tanzania has been the most productive new source of coloured stones of the last sixty years. Tanzanite comes from Merelani, sapphire from Tunduru and Songea, spinel from Mahenge, and unusual sapphire and garnet from Umba. Tsavorite garnet was first found here too. The trade runs through Arusha. This page covers each deposit and what it is known for. It sets out the treatments to expect, how labs handle Tanzanian origin, and how to buy with confidence.

The deposits

Merelani: tanzanite

Tanzanite is blue-violet zoisite from one place, the Merelani Hills near Kilimanjaro. It was found in 1967 and is mined in government-defined blocks. The stone is trichroic. It shows blue, violet and burgundy from different directions, so the way it is cut decides the face-up colour. Almost all tanzanite is heated to around 600 degrees to remove brown. The trade treats heat as standard. Labs tend to note that heating is routine rather than penalise it. Unheated blue stones are rare and hard to prove. Deep, saturated blue with a violet flash commands the top of the range. Paler lavender is plentiful. Watch for "AAA" and similar labels. They are seller words with no lab meaning. Watch too for the odd coated stone. Tanzanite is soft for a ring and cleaves. That is a wear question, not a treatment one.

Tunduru, Songea and Winza: sapphire and ruby

Tunduru, in the far south, is an alluvial field opened in the mid-1990s. It yields sapphire in almost every colour, along with chrysoberyl, spinel and garnet. Sizes are mostly small, clarity is high, and a useful share is unheated. Songea, to the west, produces small sapphires in blue-green, orange and red tones that are nearly always heated. Songea rough also fed much of the beryllium-diffused orange and yellow sapphire that appeared around 2001. Winza, near Dodoma, had a brief flare of unheated ruby and sapphire from 2007. On a report the treatment line matters more than the district. Expect heated for most Songea material, and diffusion if beryllium is present.

Mahenge and Umba: spinel and unusual sapphire

Mahenge, in the Morogoro region, produced a run of large hot pink and red spinel crystals from 2007. "Mahenge spinel" became a colour reference in its own right. Spinel is normally untreated, which is one reason it has climbed in price, though labs now check for heat. The Umba River valley near the Kenyan border has been worked since the 1960s. It is known for sapphire in orange, purple, colour-change and padparadscha-like colours, plus rhodolite and malaya garnet. Umba stones offered as padparadscha often fall outside the colour range labs accept. Ask for the report wording rather than the seller's.

Tsavorite

Tsavorite is green grossular garnet coloured by vanadium and chromium. It was first found at Lemshuko near Merelani in 1967 and later across the Kenyan border. It is not treated, so the report question is simply identity and, if you want it, origin. Clean stones above two carats are scarce and priced to match. Paler stones are sold as mint garnet, which is not tsavorite.

Arusha and how material trades

Arusha is the trade hub. Licensed brokers and dealer offices there serve Merelani and the wider country. Dar es Salaam handles export. Tanzania restricts the export of rough above set sizes. It also requires licences and government trading centres for local dealing. Buying informally from a miner is unlawful for a visitor. Much Tanzanian rough is cut in Bangkok, Jaipur and Sri Lanka. Arusha also sees material from Kenya, Mozambique and Madagascar, so a stone bought there is not always Tanzanian.

Lab origin

Tanzanite needs no origin call because it comes from one place. For sapphire, GIA, Gübelin, SSEF, AIGS, GRS and Lotus compare inclusions, trace-element chemistry and spectra with reference stones. Small East African sapphires often overlap with Sri Lanka and Madagascar. They may be reported without an origin. Spinel origin, where offered, separates Mahenge from Myanmar and Vietnam on chemistry. Origin is an opinion. The treatment finding is usually the line that moves the price.

Buying notes

Ask whether the stone is heated and which lab has seen it. If it is orange or yellow, ask whether it has been checked for diffusion. Watch for heated Songea sapphire sold as unheated Tunduru, beryllium-diffused stones sold as heated, and coated tanzanite. Mint garnet sold as tsavorite is also common, as is sapphire from neighbouring countries sold as Tanzanian.

Buying through the register

GemsVerified has checked the legitimacy, certification practice and disclosure of every dealer listed on this page. That check covers how a dealer operates, not the stones in any one parcel.

Ask for the laboratory report on any significant purchase. Confirm the treatment status in writing on the invoice. And remember that GemsVerified verifies dealers, not individual stones.