Why is tanzanite only found in one place?

It needs a specific combination of vanadium-bearing rock, pressure, temperature and metamorphic history that has been found only in a few kilometres of hills at Merelani in Tanzania. Sixty years of prospecting has turned up nothing comparable, which is why supply questions dominate its market.

Is my tanzanite heated?

Almost certainly. Rough is usually brownish, and heating to around six hundred degrees removes the brown and leaves violet-blue. The treatment is permanent, stable and standard. Untreated material of good colour is rare and comes with laboratory documentation and a large premium.

When did it become a birthstone?

In 2002, when the American Gem Trade Association added it to December. That makes it the newest birthstone apart from spinel, added to August in 2016, and many printed birthstone charts predate it.

Can I wear tanzanite daily?

Not comfortably. At hardness 6.5 with one cleavage direction and sensitivity to thermal shock, it is a special-occasion stone. A protectively set pendant or a ring worn carefully is fine; a ring worn while working will chip. Never clean it ultrasonically or with steam.

Does tanzanite have an ancient meaning?

No. It was unknown before 1967, and every meaning attached to it has been written since. That makes it a useful calibration: any source that gives tanzanite an ancient significance is inventing, which is worth remembering when reading that source on older stones.

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The gem silicates · Violet ray

Tanzanite

Tanzanite is a variety of zoisite coloured violet-blue by vanadium, and it occurs in a strip of hills a few kilometres long at Merelani near Kilimanjaro and nowhere else that anyone has found in sixty years of looking. Tiffany named it in 1968, and the American Gem Trade Association added it to December's birthstone list in 2002.

At a glance

Found in 1967 at the foot of Kilimanjaro, in one place on earth, and added to the birthstone list in 2002.

Composition: zoisite with vanadium
Crystal system: Orthorhombic
Hardness: Mohs 6.5
Family: The gem silicates
Colour ray: The violet ray
Main sources: Tanzania (Merelani), and nowhere else
Care: Hardness 6.5 with one cleavage direction. Protective settings only, no ultrasonic.

Themes

singular the recent find scarcity violet-blue one place

What it actually is

Zoisite, a calcium aluminium silicate, orthorhombic, hardness 6.5, coloured by vanadium.

It is strongly trichroic, showing blue, violet and a burgundy or brownish colour along its three crystal axes. Rough is usually brownish, and heating to around six hundred degrees removes the brown component and leaves the violet-blue the market wants. That treatment is near-universal, permanent and stable.

Cutters must decide whether to orient a stone towards blue or towards violet, and blue-dominant stones are generally worth more.

Tanzanite has one cleavage direction and moderate hardness, so it needs a protective setting and careful handling. It is also sensitive to sudden temperature change and to ultrasonic cleaning.

Where it comes from

Merelani, in the Manyara region of northern Tanzania near Kilimanjaro, is the only known source. The deposit occupies a strip of hills a few kilometres long, divided into blocks worked by both large-scale operations and artisanal miners.

The geology is specific and apparently unrepeated: a combination of vanadium-bearing rock, particular pressure and temperature conditions, and a metamorphic history that has not been found elsewhere. Sixty years of searching have produced nothing comparable anywhere.

That single-source position dominates the stone's market. Supply disruptions at Merelani affect world prices directly, and the eventual exhaustion of the deposit is a standing question in the trade.

The find is credited to 1967, with Manuel de Souza's claim the most commonly cited, and Tiffany introduced it to the market in 1968 under the name tanzanite rather than blue zoisite, which was thought unsellable.

What the traditions claimed

There is no ancient tradition and this page will not manufacture one. The stone was unknown before 1967.

What exists is a documented modern history: a commercial name chosen for marketing reasons, a rapid rise in popularity, an addition to the birthstone list in 2002, and a set of meanings assembled by crystal writers over the same period.

Those modern readings tie tanzanite to transformation, to insight and to the joining of head and heart, largely on the strength of its violet-blue colour sitting between the throat and brow assignments of the imported chakra model.

Tanzanite is the clearest case in the catalogue of a stone whose entire meaning is documented from the beginning. Nothing about it is lost in antiquity, which makes it useful for calibration: if a source gives tanzanite an ancient significance, that source is inventing, and it is worth wondering what else it invents.

How it is worked with

The singularity is the honest thing to work with. Tanzanite is genuinely from one place, in a way almost nothing else is, and that suits questions about things that cannot be replaced or repeated.

For wear, it is a special-occasion stone rather than a daily one. Hardness 6.5, one cleavage direction, and sensitivity to knocks and to temperature change all argue for a pendant or a protectively set ring worn carefully.

Never ultrasonic, never steam, and avoid sudden temperature changes such as taking a ring from a hot kitchen into cold water.

For anyone born in December, it is the newest of the month's three stones and the only one with a fixed and known origin story.

Buying it honestly

Heating is near-universal, permanent and stable, and untreated material of good colour is very rare and commands a premium with laboratory documentation.

Coated tanzanite exists, where a thin film intensifies colour, and the coating wears at facet edges.

The main substitutions are synthetic forsterite, which is grown specifically to imitate tanzanite, along with blue-violet cubic zirconia, synthetic spinel, iolite and glass.

Trichroism is the identifying test that most imitations fail: a genuine tanzanite shows markedly different colours along its three axes. Forsterite is dichroic rather than trichroic.

Price is also informative, since tanzanite has never been cheap and its single-source position keeps it from becoming so.

Handle with care

Hardness 6.5 with one cleavage direction and sensitivity to thermal shock. Never ultrasonic, never steam, avoid knocks and sudden temperature changes. Protective settings only.

Domande di riflessione

What in my life is genuinely one of a kind, and am I treating it accordingly?
If a thing has only been known for sixty years, does that make it less real?
What would I do differently if I knew the supply were finite?

Follow the thread

🔷

Iolite

The other strongly pleochroic violet-blue stone

🔵

Sapphire

The durable blue alternative

🗓️

December

Tanzanite joined the list in 2002

🪨

The gem silicates

The family this stone belongs to

🟣

The violet ray

The ray it carries

Frequently asked questions

: It needs a specific combination of vanadium-bearing rock, pressure, temperature and metamorphic history that has been found only in a few kilometres of hills at Merelani in Tanzania. Sixty years of prospecting has turned up nothing comparable, which is why supply questions dominate its market.
: Almost certainly. Rough is usually brownish, and heating to around six hundred degrees removes the brown and leaves violet-blue. The treatment is permanent, stable and standard. Untreated material of good colour is rare and comes with laboratory documentation and a large premium.
: In 2002, when the American Gem Trade Association added it to December. That makes it the newest birthstone apart from spinel, added to August in 2016, and many printed birthstone charts predate it.
: Not comfortably. At hardness 6.5 with one cleavage direction and sensitivity to thermal shock, it is a special-occasion stone. A protectively set pendant or a ring worn carefully is fine; a ring worn while working will chip. Never clean it ultrasonically or with steam.
: No. It was unknown before 1967, and every meaning attached to it has been written since. That makes it a useful calibration: any source that gives tanzanite an ancient significance is inventing, which is worth remembering when reading that source on older stones.