How tanzanite is graded, and why AAA means nothing

There is no grading scale for tanzanite. Not a weak one, not a contested one: no standard quality-grading scales exist for tanzanite at all, and GIA evaluates tanzanite but does not grade it.

This is the opposite of the situation with diamond, where a laboratory assigns a colour letter and a clarity grade from a scale everyone in the trade shares. Anybody selling tanzanite on a grade is using a scale they or their supplier made up. It may still be an honest description of their own stock. It is not a measurement, and it cannot be compared with anybody else’s.

What does AAA tanzanite mean?

Whatever the company using it decided it means.

GIA’s answer to this exact question is unusually direct: individual companies might create their own quality descriptions, like AAA, AA and A, to denote the range of quality of their goods, and no standard scale sits behind any of them.

So AAA is not a lie, and it is not information either. It tells you where a stone sits within one seller’s inventory. Two AAA tanzanites from two merchants can be visibly different stones at different prices, and neither merchant has done anything improper.

The practical consequence is that a grade in a listing is not a reason to buy and not a reason to pay more. Ask what the seller means by it, and expect an answer about colour rather than about letters.

Why diamond has a scale and tanzanite does not

Because diamond is nearly uniform material and tanzanite is not.

A diamond grading scale works because the thing being graded barely varies. Colourless diamond is one material, judged on how far it departs from colourless, and two stones of the same grade really are comparable. Tanzanite is the opposite case on almost every axis.

Aspect	Diamond	Tanzanite
Colour origin	Intrinsic to the crystal	Vanadium, plus heat applied by people
Colour direction	One colour, whichever way you look	Trichroic: blue, red-violet and yellow-green down three axes
Who decides the face-up colour	The crystal	The cutter, when orienting the rough
Effect of size on colour	None	Deep saturation generally needs above five carats
Standard scale	Yes, shared across the trade	None exists

Read down that middle column and the scale makes sense. Read down the right-hand one and it stops making sense: you would be grading a colour the cutter chose, at a saturation the carat weight partly caused, seen down one of three axes, under whatever light happens to be overhead.

A letter cannot carry that. What can carry it is a description of the specific stone, which is why the useful question to a seller is never “what grade is it” but “why does this one cost more than that one”.

What a laboratory report does tell you

Identity, treatment, and the measurable facts. Not quality.

A GIA Colored Stone Identification Report assesses weight, measurements, shape, cutting style and colour; identifies whether the stone is natural or laboratory-grown; and names any detectable treatments.

Read that list for what is missing. There is no verdict on whether the colour is good, no clarity grade, no ranking. The report establishes what the stone is and what has been done to it, which is the part a buyer genuinely cannot determine for themselves. Whether it is beautiful is left where it belongs.

It is worth asking for one anyway. Identity matters more here than people expect: zoisite is occasionally found in pink, green and yellow, and although some sellers call those tanzanite, GIA calls them zoisite.

What you are actually protected against

Not a bad stone. A different stone.

The risk a report removes is misidentification, and it is a real one here because no synthetic tanzanite is known, but many simulants do exist. A simulant is a different material chosen to look similar: synthetic forsterite, coated glass, and blue-violet cubic zirconia all appear under names built to sound adjacent to the real thing.

Nothing about a grade helps you here. AAA on a ticket is a claim about quality within a seller’s own stock, and it is perfectly compatible with the stone not being tanzanite at all. Identity and quality are separate questions, and only one of them has an authority behind it.

The physical facts a laboratory measures are what settle it. Tanzanite has a specific gravity of 3.35 and a refractive index between 1.692 and 1.700, and neither figure is a matter of opinion. A stone that fails them is not tanzanite regardless of what the label says, and a stone that passes them is, regardless of whether anybody likes its colour.

Why heat treatment barely moves the price

Because almost everything has been heated, and because the laboratory often cannot tell.

Untreated tanzanite is typically brownish, and most blue tanzanite on sale owes its colour to heat treatment. The stones first found at Merelani were an exception, having probably been heated naturally within the earth.

Two things follow, and the second is rarely said aloud. Trade professionals assume the majority of tanzanite on the market has been heated in some way, so there is little effect on pricing. And in many cases it is challenging for gemmological laboratories to determine whether a tanzanite has been heated.

That is why a report names detectable treatments rather than certifying an absence. Anybody charging a premium for guaranteed-unheated tanzanite is selling a certainty the laboratories themselves are careful not to claim.

So how do you compare two stones?

By looking at them, in the order that matches how price is actually set.

What to judge	What you are looking for
Colour	Saturation first. Exceptional stones are an intense violetish blue with red flashes of pleochroic colour from within; paler colours are more available and more affordable
Cut	Even return of light across the whole face. Cutting decides the face-up colour, so a badly oriented stone wastes good rough
Clarity	Most faceted tanzanite has no eye-visible inclusions, so anything you can see unaided causes a drop in value. Fractures matter most, because they are a durability problem too
Carat	The finest and deepest colours are usually seen above 5 carats, so size and colour are one judgement, not two

Compare stones side by side, in the same light, at the same time. Tanzanite’s colour depends on the light it is under, so two stones judged in two rooms on two days have not been compared at all.

How to read a listing when the grade means nothing

Ignore the letters and read the four things underneath them.

Most tanzanite listings carry a grade, a carat weight, a shape and a price, and only three of those are information. What you want from the description is enough to picture the stone, and there are specific words worth looking for.

Look for a colour described in two parts rather than one. “Violetish blue” and “bluish violet” are not the same stone, and a seller who writes only “blue” is either not looking carefully or not telling you which way it leans. Exceptional stones are an intense violetish blue with red flashes of pleochroic colour from within, and that sentence is the standard a description should be measured against, not a letter.

Look for the lighting the photograph was taken in. Tanzanite reads differently in daylight and under fluorescent light, so a listing that does not say which is showing you one of the stone’s faces and calling it the stone. A seller who volunteers “photographed in daylight, and it reads more violet indoors” is being straight with you, and that sentence is worth more than any grade on the page.

Look for what is said about inclusions. Most faceted tanzanite has no eye-visible inclusions, so anything you can see unaided causes a drop in value. A listing that says “eye clean” is claiming the ordinary case. A listing that describes what is visible and where is claiming something harder and more useful.

Look for the treatment sentence. It should exist, it should say heated, and it should not be dressed up. Anything else needs a report.

What actually moves the price

Colour, then size, and the two are not separable.

The four factors are the same ones used for any coloured stone, but their weight is unusual here. Colour carries most of the price, and within colour, saturation carries most of the weight. A vivid medium-toned stone will outprice a larger pale one of the same shape and clarity, which is the opposite of how most people expect carat weight to behave.

Size then re-enters through the back door, because saturation partly depends on it. The finest and deepest colours are usually seen above five carats, which means a large vivid stone is expensive twice: once for being large, and once for being the size at which the colour becomes possible at all. Two stones can differ by a factor of ten in price for reasons that are entirely about those two lines interacting.

Cut is the factor most often undervalued by buyers and most consequential in the hands of the cutter. The orientation chosen before the first facet decides which of the three pleochroic colours dominates the finished stone, and a cutter chasing weight rather than colour can turn good rough into a stone that looks flat face-up. You cannot see that decision directly. What you can see is whether the stone returns light evenly across its whole face, which is the visible symptom of it having been cut properly.

Clarity moves the price least, and only in one direction. It is close to a pass or fail: eye-clean is expected, and anything visible costs. Where clarity earns real attention is when what you are seeing is a fracture rather than an inclusion, because that is a durability question wearing a clarity question’s clothes.

Two stones, one worked example

The point of all of this is a decision, so here is one.

Put a 3 carat vivid violetish blue stone next to a 7 carat pale one, both eye-clean, both well cut, and both honestly described. The larger stone weighs more than twice as much. Depending on the market, they can be priced within a few hundred euro of each other, and neither seller is doing anything wrong.

The three carat stone is the rarer object: at that size, deep saturation is against the odds, so the colour is doing something unusual. The seven carat stone is the more impressive object on a hand, and its paleness is the ordinary case rather than a fault. Which is the better buy depends entirely on whether you are buying colour or presence.

No grading scale could answer that, and this is the reason one has never been agreed. The letters would have to encode a preference, and a preference is not a measurement.

What comparing by eye cannot do

It cannot tell you about the inside of the stone, and it cannot protect you from your own lighting.

Two things are invisible to an unaided comparison however careful you are. The first is treatment: in many cases it is challenging for gemmological laboratories to determine whether a tanzanite has been heated, so an eye across a counter has no chance at all. The second is durability. A fracture reaching the surface is a clarity feature you might spot and a structural weakness you probably will not weigh correctly, and with perfect cleavage in one direction the difference matters more here than it would in a sapphire.

There is a third limit, and it is the one that catches experienced buyers. You cannot compare a stone you saw last week against one in front of you now. Tanzanite reads sapphire blue in natural light and violet under fluorescent light, which means memory is not a reliable instrument for this stone. If two candidates cannot be put side by side in the same light, the comparison has not happened, and no amount of confidence substitutes for it.

This is where a seller who will talk to you is worth more than a certificate. If you want to see how we set that out, including the questions our own suppliers have not answered: every piece the maison sells, and how we choose them.

The thing no report will settle

Whether the stone is worth what is being asked.

This is not a gap in the system; it is what a coloured stone is. Grading exists for diamond because the material is close to uniform and the differences are small and countable. Tanzanite is pleochroic, cut to a judgement call, and priced on an impression of colour that changes with the bulb overhead. A scale would flatter it and mislead you.

What replaces the scale is a seller who will explain the trade-offs in the stone in front of you. Much of what they should be explaining was decided long before the stone reached a window: how a tanzanite is cut and set covers the orientation choice that fixes a stone’s colour permanently. Because there is no scale, there is also no price list, and what decides the price of a tanzanite explains what a quote is actually built on. If you want the background first, start with what tanzanite is and what decides its colour. And if the stone is going into a ring worn every day, durability belongs in the judgement alongside colour: tanzanite engagement rings, and when the answer is no.