Tanzanite, the stone that only comes from Tanzania, and what it is really worth

The question nearly always comes up in the car. Somebody has walked past a shop window in Arusha, or a guide has mentioned the stone, and by the afternoon somebody in the back wants to know whether they should buy one.

We live in Moshi, about 40 kilometres, 25 miles, from the only place on earth this stone is mined commercially. We are not jewellers and we do not sell stones. What we do have is years of hearing what guests paid in Arusha and what their appraiser said about it when they got home. So this page is about what tanzanite is, what it costs here, what it turns out to be worth there, and what you need on paper to get it out of the country.

One thing first, because it is our own correction. This site used to say tanzanite is a thousand times rarer than diamond, and that the mines were nearly empty. We went and checked both. Neither holds up, and the reasons are further down.

What tanzanite is

Tanzanite is the blue to violet variety of a mineral called zoisite. The colour comes from traces of vanadium sitting where aluminium would normally be in the crystal structure. Zoisite itself turns up in other places and other colours, pink thulite, or the green anyolite with ruby in it, but gem-quality blue zoisite comes from one area and nowhere else.

That area is Mererani, in the hills by the Lelatema mountains in Simanjiro district, about 40 kilometres, 25 miles, southeast of Arusha. You will see the deposit described as 7 by 2 kilometres, as 4 by 2, as 6 by 2, and as eight square miles, depending on which source you read. The honest description is a strip a few kilometres long and about two kilometres wide, a little over a mile. No other gem-quality blue zoisite is known to be traded anywhere in the world.

The stone is around 585 million years old, formed in metamorphic rock under heat and pressure in the middle of the Ediacaran. It has been sitting in that strip of ground since long before anything with a backbone walked on it.

Those last two rows matter more than they look. A hardness of 6 to 7, where diamond is 10, together with perfect cleavage in one direction, makes tanzanite vulnerable in a ring you wear every day. Door frames and car door locks are what break them in practice. A pendant or a pair of earrings is a safer setting for this stone, and if you do want a ring, it needs a setting that protects the edges.

Why it changes colour

Unheated tanzanite is trichroic, which means three different colours show along the three axes of the crystal, a red-violet, a deep blue and a green-yellow. After heating two of them remain, the blue and the violet, and those shift as you turn the stone or carry it from daylight into lamplight. That is not a trick of the setting. That is the crystal.

Which means the cutter decides what colour your stone is, by choosing which axis faces up. The bluest orientation usually costs the most weight, and since stones are priced per carat, there is a standing incentive to keep the weight instead. That is why two stones out of the same mine, in the same shop, can look so different.

Why almost every stone has been heated

Rough tanzanite is reddish brown, and sometimes nearly colourless. Heating it to several hundred degrees changes the oxidation state of the vanadium, which takes out the yellow and brown and leaves the blue that people want.

Sources give the temperature as anywhere from about 300 to 600 degrees Celsius, so we are not going to print an exact figure. What they agree on is that this is low compared with what sapphire needs, and that heating or cooling the stone too fast will crack it.

Work on the assumption that every blue or violet tanzanite you are shown has been heated. That is the norm in the trade, not a defect, and the treatment is stable and permanent. It is also undetectable, which matters for the next paragraph. Some of the earliest stones lay near the surface and had been heated naturally, probably by a bush fire, and those came to be called D-Block. That is a trade label with no gemmological meaning whatsoever.

So two things follow. A premium charged for unheated blue tanzanite is a premium for a claim that no laboratory on earth can confirm. And D-Block is not a reason to pay more.

What is a real problem is coating. Cobalt-coated tanzanite has been documented by both the AGTA and the AGL. The coating wears off with use, and only XRF analysis in a laboratory will find it. So ask for it in writing: have the invoice state whether the stone is heated and whether it is coated.

How rare it is, and how rare it is said to be

You will read everywhere that tanzanite is a thousand times rarer than diamond, and until recently you read it on this site too. The figure traces back to marketing by TanzaniteOne, which used to operate the largest mine, and by the Tanzanite Foundation. No method behind it has ever been published.

The production figures tell a different story. Tanzania’s record year was 2019, at 781.2 kilos, roughly 3.9 million carats. World rough diamond production in 2024 was around 118 million carats. That is a factor of tens, not a factor of a thousand. The comparison is imperfect, because a lot of both totals is low-grade material, but it is nowhere near the claim.

Here is what is true, and it is better than the invented number. Tanzanite comes from one source, and geologists do not expect a second one to be found. That is unusual in geology, and it is the real reason the stone is special. It does not need a multiplier.

And no, the mines are not nearly empty

Around 2010 The Tanzanite Experience said there would be nothing left within twelve to fifteen years. That window has closed, mining is still going, and the same prediction keeps being republished with a fresh number attached, ten years, twenty, thirty.

The government figures say something else. The National Bureau of Statistics put reserves in 2018 at 109 million carats. Block C on its own was put at 87.1 million carats, with a life expectancy running into the 2040s. Shafts had reached 900 metres, nearly 3,000 feet, by 2014, and geological study has identified tanzanite-bearing layers down to 2,000 metres, about 6,500 feet.

So the deposit is finite, which is not in dispute, and the largest mine expects several more decades out of it.

That removes the oldest argument in the shop, which is buy now before it runs out. If somebody says that to you across a counter, you now know where the line comes from.

Who found the stone

The Western literature names Manuel de Souza, a tailor and gold prospector of Goan origin living in Arusha. In July 1967 he came across blue crystals, took them first for olivine and then for dumortierite, and registered the first mining claims over the ground.

That is the version in every jewellery book, and it is not the whole story.

Jumanne Mhero Ngoma found blue stones near Mererani in January 1967, six months earlier. He was twenty-eight years old. In 1970 President Nyerere gave him a certificate of recognition and fifty thousand shillings. In 1984 the Tanzania Commission for Science and Technology issued him a certificate for scientific discovery. In April 2018, fifty-one years after the find, President Magufuli gave him a hundred million shillings. He died in January 2019, the year after.

The Tanzanian state recognises Ngoma as the man who found it. Almost nobody outside Tanzania has heard his name.

Ian McCloud, a government geologist in Dodoma, made the first correct identification of what the mineral was. Samples went out through the Nairobi geologist John Saul to the GIA in the United States, and on to Harvard, the British Museum and Heidelberg University.

The name is Tiffany’s. Henry B. Platt, vice-president of the company and the great-grandson of Louis Comfort Tiffany, decided that blue zoisite would never sell, and that a new name could carry the single origin with it. Tiffany launched it in 1968 with the line that it was found in two places, Tanzania and Tiffany’s.

There are other versions, including a Maasai herder who found blue stones after a bush fire. That story fits the near-surface stones that had been naturally heated, so it is plausible, and we could not find a source for it, so we are not presenting it as fact. The honest position is that three men have a claim on this and the credit has never been settled.

Who earns from it today

Block C, the largest mine, has been held since around May 2022 by Franone Mining and Gems, which is a hundred percent Tanzanian-owned and won it through a government tender. Before that the owners were South African, then British, then a joint venture with the state company STAMICO.

Most of the stone does not come from there. Hundreds of independent shafts supply something like eighty percent of annual production. That single fact explains two things you will notice as a buyer: why the same stone carries a different price in two shops on the same street, and why paperwork about where a stone came from is so rare.

In June 2020 a small-scale miner called Saniniu Laizer sold two rough stones, 9.27 and 5.103 kilos, about 20 and 11 pounds, to the government for 7.74 billion shillings, roughly 3.35 million dollars. Within three weeks his company found a third record stone, which took the total past five million. He runs an operation of more than two hundred people, and it was his employees who found them. The American jeweller Le Vian said afterwards that what he was paid was a fraction of the retail value.

Laizer made headlines around the world because he is the exception. He is not the rule, and it is worth holding both of those in mind at once.

What decides the quality

Colour. A deep, saturated blue-violet is what the market wants. A pale violet stone is worth a great deal less. Saturation matters more than the exact hue, which is the opposite of what most buyers assume.

Clarity. The GIA treats tanzanite as a stone that is normally eye-clean, so visible inclusions cut the price sharply rather than gently.

Cut. This decides how much light comes back out at you, and as above, the cutter’s choice of orientation is also what set the colour in the first place.

Weight. One carat is 0.2 grams. The price per carat steps up at one, two and three carats, and then changes surprisingly little from there up to about twenty.

Why there is no official quality figure

Diamonds have a grading system the whole world accepts. Coloured stones have nothing of the kind. Which means that any scale you are shown for tanzanite was produced by somebody with an interest in the sale.

AA, AAA and AAAA are not standards. The Tanzanite Experience, one of the larger sellers in Arusha, wrote on TripAdvisor that AAA is, in their own words, a street term that they use for rough tanzanite, and that it is very limiting when applied to finished stones. That is the seller saying it, not us.

The Tanzanite Foundation has its own colour scale. It is connected to the former owner of the mine, so it comes from the selling side rather than from an independent institute.

What works instead is simple and nobody tells you to do it. Bring a colour reference from home, something you already know you like, and compare in daylight rather than under the shop’s lighting. A traveller on TripAdvisor put it better than we can: absolutely bring it from home.

What tanzanite costs

There is no public price index for this stone. Every figure below comes either from somebody selling or from a single buyer reporting what they paid, so read them as orders of magnitude and not as a price list.

Is it cheaper in Tanzania

There is no evidence that Arusha is cheaper than London or New York, and there is reason to expect the opposite. Travellers report the reverse, and one was told a per-carat price above six hundred dollars that was higher than what they could find at home.

The margin sits in four places. Tourist pricing quoted in dollars. VAT, which is eighteen percent on the mainland and fifteen percent on Zanzibar. Commission paid to whoever brought the customer through the door. And discount theatre, where the first number you hear was never the real one.

Buying at the source can work out well for an informed buyer who finds the right dealer. It has never been shown to work out well for the average traveller, and we would rather you knew that before you walked in than after.

What it is worth once you are home

Some travellers have had their stones appraised after they got home and published what they were told. Five of those cases are documented well enough to put in a table.

The appraisals land between 36 and 60 percent of what was paid. And an insurance appraisal normally sits above resale value, because it has to cover replacing the thing, so what you could sell it for would be lower again.

Why this is not only the shops

There is no tanzanite exchange, no auction open to private individuals, and no price index. So there is no market in which an owner can sell a stone at a knowable price. That is the structural problem, and it exists whoever sold you the stone.

An American appraiser worked out that at a normal retail margin, the intrinsic value of the stone has to triple before the buyer gets their own money back.

Prices have also fallen more than once. After 2001, then again in 2008 and 2009 by twenty to thirty percent, and by up to half for the lower grades, and again in 2020 when cruise-ship sales stopped.

The rises you will read about do not survive a check. A Dutch dealer claimed in 2016 that prices had risen fifty percent in ten years, and two hundred percent for AAA, with no source given. An investment site cites a GIA Investment Analysis 2024 showing twenty-five percent a year. That publication does not exist, and the GIA does not produce investment analyses.

So the conclusion is the one nobody selling you a stone will reach. Tanzanite is not an investment. Only exceptional top stones, bought at wholesale by people who do this for a living, hold their value. Buy it because you like looking at it, and assume a resale value of zero.

Buying tanzanite in Tanzania

If you are going to buy one, buy it well. This is what we would ask, in the order we would ask it.

Before you leave home

1. Bring a colour reference, something you already know you like the look of.
2. Set a budget, and set it on the assumption that the resale value is zero.
3. A dichroscope costs very little and fits in hand luggage. Tanzanite shows two different colours through its two windows. Glass, cubic zirconia and synthetic spinel show the same colour in both.

In the shop, ask these

1. What is the exact weight, and is this stone heated, or coated? Have the answer printed on the invoice, not given to you verbally.
2. Which laboratory issued the certificate, and is that laboratory independent of this shop?
3. Can I return the stone within a set period if an independent laboratory finds something different?
4. Will you arrange the export permit and the Certificate of Origin, and what do those cost?
5. Are VAT and the royalty shown separately on the invoice?
6. Does my guide or driver receive a commission on this purchase?

That last question is not an insult and nobody will take it as one. Shops in this market commonly pay a percentage to whoever brings a customer in, and that percentage is built into the price you are quoted. If you would rather not have it in there, go on your own and choose on your own.

Red flags

1. Buying on the street or in a market. You will almost certainly not get what you think you are getting.
2. A discount of fifty percent or more offered as the opening position.
3. Any pressure to decide today.
4. A certificate that states a monetary value.
5. Unheated blue tanzanite, or D-Block, or AAA, used to justify a higher price.
6. Payment with no invoice, or cash with no receipt.
7. Rough stones above the legal weight limit, which is the next section.

What a certificate does and does not tell you

An independent laboratory, the GIA or the AGL, or in Europe SSEF, Gübelin or HRD, establishes what the stone is and whether it has been treated. That is what a certificate is for.

It does not establish what the stone is worth at retail. A certificate carrying a monetary value is a sales document. The 2017 buyer in the table above paid 1,600 dollars holding a certificate that suggested at least double that, and a Canadian gemmologist put it at no more than 600.

Some shops in Arusha have a laboratory in the same building. That can confirm what the stone is and what it weighs, which is worth having, and it is not an independent appraisal of value.

If you want certainty, have the stone assessed by a laboratory with no stake in the sale, either here or at home.

Getting it out of Tanzania, and through customs at home

There are two pieces of paperwork, one at this end and one at yours, and almost nobody writes the first one down.

Out of Tanzania

Under the Mining (Mineral Trading) Regulations 2010, a visitor on a tourist visa may export minerals up to twice a year, with an export permit, up to a value of a thousand dollars. Above that figure a higher fee applies, or a separate permit from the Commissioner for Minerals.

Every tanzanite export permit comes with a Certificate of Origin. Ask the shop whether they handle that for you and what it costs, before you pay for the stone rather than after.

Rough stones carry a weight limit, which exists to keep the cutting work in Tanzania. Sources quote one gram and two grams and we could not confirm the current figure from the regulation itself. Cut stones are not covered by it. If you want to take rough stone out, ask the Mining Commission before you buy.

Travel with the invoice, the export permit, the Certificate of Origin, proof of payment and any laboratory certificate. The paperwork that gets the stone out is also the paperwork that proves what you paid, which is what you will want at the other end.

Into your own country

This is where we stop giving you figures, deliberately, because you are reading this in one of four or five different countries and the numbers are different in all of them. What is the same everywhere is that a tanzanite worth having will cost more than your personal allowance, so this is not a question you can skip.

Check your own customs authority before you buy, not after you land. For the United States that is Customs and Border Protection, for the United Kingdom HMRC, for Canada the Canada Border Services Agency, and for Australia the Australian Border Force. Two things catch people out often enough to be worth knowing in advance: allowances are set per person and in most countries cannot be pooled to cover one expensive item, and a single item over the limit is frequently taxed on its whole value rather than on the excess. Both of those are worth confirming for your own country, because they are what turns a souvenir into a bill.

Declare it. The paperwork you collected in Arusha is exactly what a customs officer wants to see, and walking past the desk hoping to be waved through is, in a number of countries, legally the same as declaring that you have nothing.

And check your insurance. Travel policies tend to have low limits for valuables, and cover for valuables usually needs an appraisal report, which means getting the stone appraised at home anyway. Which, as the table further up shows, is also the moment you find out what you bought.

December birthstone

In October 2002 the American Gem Trade Association added tanzanite to the December birthstones, alongside turquoise and zircon. The International Colored Stone Association and Jewelers of America backed the change.

You will often read that this was the first change to the birthstone list since 1912. That is the AGTA’s own wording and it is not accurate. The list was amended in 1952, which is when alexandrite, citrine and pink tourmaline went on it, and spinel was added for August as recently as 2016.

So it is a lovely stone for a child born in December, and it has only been on that list this century.

What makes tanzanite worth knowing about is not a multiplier and not a prediction about running out. It is one strip of ground a few kilometres long, in hills we drive past every week, and nowhere else on the planet. That stays true whether the stone costs two hundred dollars a carat or eight hundred.

If you buy one, you are buying the memory of a place rather than an asset. We do not think that is a lesser reason. It is just the honest one.

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