Buying Tanzanite in Tanzania
A gemstone found in one place on earth, in the hills near Merelani. How the trade works, how stones are graded, and what a certificate does and does not tell you.
Tanzanite comes from a single small deposit near the Mererani Hills in the Manyara Region and from nowhere else on earth. This guide covers what the stone is, how it is mined, why nearly every one has been heat treated, how to read a laboratory report properly, and the sales lines worth recognising before you buy.
Safaris That Include Tanzanite
A Guide to Tanzanite in Tanzania
What tanzanite actually is
Tanzanite is the blue and violet variety of a mineral called zoisite, and its colour comes from small quantities of vanadium in the crystal. That sounds like a technicality until you see a piece of rough turned in the hand, because the stone's defining property follows directly from it.
Untreated tanzanite is trichroic. Looked at along different crystal axes, the same stone shows blue, violet and a brownish burgundy. A cutter therefore has to decide which of three colours the finished gem will face up as, and that decision is made before a single facet is placed. After heat treatment, which almost every stone on the market has had, it becomes dichroic, running from violet through bluish violet to indigo and blue.
This is why two tanzanites of similar size can look so different, and why the stone rewards being looked at under more than one light and from more than one angle before anyone commits to it. Turn it. If a seller is reluctant to let you turn it, that tells you something.
Merelani, and what a single source deposit really means
Tanzanite comes from one place on earth: a strip of ground in the Simanjiro District of the Manyara Region, near the Mererani Hills, within sight of Kilimanjaro. The productive area is roughly seven kilometres long and two wide. There is no second deposit anywhere.
Geologically it is a product of the Mozambique Orogenic Belt, a zone two to three hundred kilometres wide running north to south through eastern Tanzania, which was folded, faulted and metamorphosed through repeated cycles. The gems sit in pockets inside fractured segments of pegmatitic vein, and finding them is a matter of following a seam through rock rather than sieving gravel.
Since 1990 the ground has been divided into four mining blocks, A, B, C and D, worked by a mix of larger mechanised operations and very large numbers of small scale miners.
Now the part that matters commercially. Because there is only one deposit, tanzanite is sold with an urgency that no other coloured stone carries: that supply is nearly exhausted, that this is the last generation who will be able to buy it, and that prices can only rise. It is worth knowing that the published figures do not support that story. A 2018 assessment put total reserves at around 109 million carats, with the life of mine on Block C expected to run into the 2040s. Single source is a real and interesting fact about tanzanite. Imminent scarcity is a sales line, and it is the most effective one used on visitors.
Nothing in this guide should be read as a view on tanzanite as an investment. Buy it because you want to look at it.
The discovery, and the name
The stones were recognised in January 1967. The discoverer recognised by the Tanzanian government is Jumanne Mhero Ngoma, who came across them in the Mererani hills and was honoured by President Nyerere three years afterwards. As with most mineral discoveries, several people have claimed to have seen it first, and the account you hear on any given day will depend on who is telling it.
The name is not Tanzanian in origin. Henry B. Platt, a vice president of Tiffany and Co and a great grandson of Louis Comfort Tiffany, judged that a gem called blue zoisite would not sell, and renamed it after the country it came from. The advertising line was that it could be found in two places, Tanzania and Tiffany's. It worked, which is why a mineral that had been out of the ground for barely a year arrived in the world already famous.
How it comes out of the ground
This part is usually left out, and a buyer ought to know it.
Much of the deposit is worked by small scale miners in conditions that first hand gemmological accounts describe in detail. In Block D, reported to be worked by five to six thousand miners, vertical shafts run around a hundred metres down and are descended by wooden ladders. From the bottom, secondary tunnels extend two to three hundred metres to the working face, and much of that distance is passable only by crawling, in passages often no more than a metre high. The rock carries heavy graphite dust, the heat underground is severe, and dust masks are frequently removed simply in order to breathe. Miners have been described emerging at the end of a shift too exhausted to lift a cup of water.
Flooding is a recurring danger. After heavy rains, Merelani mines have flooded with miners trapped underground and lives lost. The published accounts available do not give reliable dates or death tolls for individual incidents, so none is stated here.
In April 2018 the government built a perimeter wall around the mining area, roughly twenty four kilometres of it, constructed in about three months by some two thousand National Service personnel, with the stated aim of controlling smuggling and improving security. Recorded production rose sharply afterwards, from 147.7 kilograms in 2018 to 781.2 kilograms in 2019, though a rise in recorded output and a rise in actual output are not the same thing.
None of this means a buyer should not buy tanzanite. It does mean the phrase ethically sourced, used without specifics, is doing no work at all. A seller who can tell you which block a parcel came from and who they bought it from is telling you something. A seller who says only that it is ethical is not.
Heat treatment, and why nearly every stone has had it
Most tanzanite comes out of the ground with a brownish cast. Heating it to somewhere between 370 and 390 degrees for about half an hour removes that and brings out the blue and violet. The treatment is stable, permanent and standard.
Three consequences follow, and they are the practical heart of buying one.
First, the trade assumes tanzanite has been heated, so heating has little effect on price. A seller presenting heat treatment as a defect to be discounted, or as a special feature, is either confused or working an angle.
Second, and more importantly, GIA notes that it is frequently difficult even for gemmological laboratories to establish whether a given tanzanite has been heated. This matters enormously, because it means a claim that a stone is rare unheated material is often a claim that cannot be conclusively tested. Treat any premium asked for unheated tanzanite with real caution, and do not pay it on a seller's word.
Third, because the treatment is universal and expected, its disclosure is not usually the thing that goes wrong in a tanzanite sale. What goes wrong is identity and paperwork.
What actually determines quality
The stone is assessed on the same four properties as any coloured gem, but they behave unusually here.
- Colour is the dominant factor. The most valued material is an intense violetish blue, and the finest stones show flashes of the pleochroic colours as they move. Pale or greyish stones are far more common than the marketing suggests.
- Clarity matters because most gem quality tanzanite has only microscopic inclusions, so anything visible to the eye stands out. Fractures in particular reduce value sharply, and they also make a stone more vulnerable, since tanzanite is not a hard gem.
- Cut carries more weight here than in almost any other stone, because the cutter chose which pleochroic colour to present. A well cut tanzanite faces up blue-violet from the table. A badly cut one shows its brown or grey axis and no amount of setting will rescue it.
- Size interacts with colour rather than standing alone. Deeper, more saturated colour is typically found in larger stones, which is why small tanzanite is often noticeably paler than the pictures people have in mind.
Look at any stone you are considering in daylight and under artificial light, and rotate it. Tanzanite's appearance shifts more between light sources than most buyers expect, and a stone bought under a shop's carefully chosen lamps can be a disappointment at home.
Certificates, and how to use one properly
A certificate is only as good as the laboratory that issued it and your ability to confirm it independently. A printed document in a plastic sleeve proves nothing on its own, and forged and meaningless paperwork is a well known problem in this trade.
The way to use one:
- Note the issuing laboratory and the report number. Internationally recognised laboratories, GIA among them, publish a report lookup service so that a number can be checked against the laboratory's own record.
- Check the report yourself, on the laboratory's own website, typing the address in rather than following a link or a QR code supplied by the seller.
- Read what the report actually says. A report describes the stone examined. It is not a valuation, it is not a guarantee of price, and it does not by itself prove that the stone in front of you is the stone the report describes. Match the weight, the measurements and the described characteristics to what you are holding.
- Be sceptical of unfamiliar laboratory names, of documents that state a monetary value, and of anything described as a government certificate of authenticity.
- If a stone is significant to you, the safest route is to buy it and have it independently examined afterwards by a laboratory or a qualified gemmologist of your own choosing, and to agree before purchase what happens if it does not check out.
Where people buy, and the pressure that comes with it
Tanzanite is sold everywhere a visitor goes in northern Tanzania: shops in Arusha and Moshi, lodge gift counters, curio stalls, airport concessions and by individuals who approach travellers directly. The Tanzanite Experience, a retailer on India Street in Arusha, also runs an exhibition about the stone. That is a factual description of what it is rather than a recommendation. No dealer is recommended on this site.
Buying practices worth keeping to:
- Never buy a gemstone from someone who approaches you in the street, however good the story. This is the origin of most of the bad outcomes.
- Do not buy under time pressure. Closing today, last stone of this grade, the price goes up tomorrow: all of these are techniques, not information.
- Buy from a seller with a fixed, findable business address you could return to, and get a receipt that describes the stone properly, including weight, dimensions, treatment status and the price paid.
- Airport purchases combine the highest pressure with the least ability to examine a stone, compare it or go back. That is a bad combination for an expensive decision.
- Take your time. There is a great deal of tanzanite in Tanzania and there will be more tomorrow.
Taking a stone home
Tanzania regulates the export of gemstones, and the rules sit with the mining authorities and customs rather than with a shop. The specific current requirements change, so confirm them rather than relying on a general description, including one found here. For the customs side of the same question, the revenue authority's published allowances and the currency rules are set out with what could and could not be sourced.
What is sensible regardless: buy from a seller who can supply proper export documentation and is willing to explain it, keep the receipt and any laboratory report with the stone rather than packed away, declare the purchase where you are required to, and check your own country's import rules and duty thresholds before you travel home. If a seller suggests carrying a stone out without documentation, that is not a shortcut being offered to you, it is a risk being transferred to you.
For anyone whose interest in tanzanite is geological rather than acquisitive, the stone's context sits alongside the other things the north is known for: the same region covers archaeological tours at Olduvai and Laetoli, and the museum tours guide covers where the country's collections are held.
Questions buyers ask
Is tanzanite really about to run out?
The published figures do not support the urgency. A 2018 assessment put reserves at around 109 million carats with the main block expected to produce into the 2040s. Tanzanite genuinely comes from only one deposit, but that is not the same as imminent exhaustion, and the two are frequently blurred by sellers.
Has my stone been heat treated?
Almost certainly, and that is normal. Heating at around 370 to 390 degrees is standard practice and the trade assumes it. What is worth treating carefully is the opposite claim, that a stone is unheated, because laboratories often cannot establish that conclusively either way.
Is it cheaper to buy in Tanzania?
This guide does not deal in prices, and a price comparison made from a shop counter in Arusha is not a reliable basis for a decision anyway. The more useful question is whether you can verify what you are buying, and that depends on the seller and the paperwork rather than on the country.
How do I know it is tanzanite at all and not something else?
You mostly cannot, by eye. Several materials resemble it. The protection is a report from a recognised laboratory whose number you have checked yourself on that laboratory's own site, matched against the stone's weight and measurements, or independent examination after purchase on terms agreed beforehand.
Can I visit the mines at Merelani?
The mining area is enclosed by a perimeter wall and is a working industrial and small scale mining site, not a visitor attraction. Treat any offer of an informal mine visit with considerable caution. The exhibition attached to a retailer in Arusha is the usual substitute.
Is tanzanite hard enough for an engagement ring?
It is softer and more prone to fracture than the stones usually chosen for daily wear, which is why fractures affect its value so much. If it is going into a ring that will be worn every day, discuss the setting and the protection of the stone with the jeweller rather than assuming it will behave like sapphire.
What does ethically sourced mean when a seller says it?
On its own, very little. Conditions for small scale miners at Merelani are documented as severe. A seller who can say which block a stone came from and who they bought it from is giving you information. A seller offering only the phrase is not.
Should I buy tanzanite at the airport?
It combines maximum time pressure with minimum ability to examine, compare or return. If you want a stone, buy it earlier in the trip from a seller with a fixed address you could go back to.