Tanzanite colour grading explained
There is no universal grading standard for tanzanite colour. Laboratories describe hue, tone and saturation; the trade adds labels such as AA, AAA and AAAA, which are sales terms with no agreed definition. The most valuable stones are vivid, medium-toned violet-blue to blue, saturated and lively in ordinary daylight.
- Hue is the colour itself, tone is how light or dark, saturation is how pure and intense.
- "AAA" is a seller’s label, not a laboratory grade — always ask what it means in their own words.
- Top value: vivid, medium tone, blue with a violet secondary, no grey.
- Judge colour in daylight, not under a jeweller’s spotlight.
The three things that make up colour
Hue is which colour you see: tanzanite runs from blue with a violet secondary to violet with a blue secondary. Tone is how light or dark the stone is, from pale to nearly inky. Saturation is how pure the colour is, and grey is its enemy — a greyish stone reads dull no matter how deep it looks.
The commercial peak is a vivid, medium to medium-dark stone whose main hue is blue. Stones that read mainly violet are beautiful and usually cost less, which makes them the best value in the material.
Why pleochroism complicates everything
Tanzanite shows different colours down different crystal directions: blue, violet and, before heating, a brownish burgundy. The cutter decides which colour faces up, and that decision is permanent. It is also why the same stone can look blue in the seller's photograph and violet on your hand — both images can be honest.
What the trade labels actually mean
| Label you will see | What it usually signals | What to ask |
|---|---|---|
| AA | Pale or greyish commercial material | Daylight photo and video, unretouched |
| AAA | Good blue, the most used label in online listings | Hue, tone and saturation in words |
| AAAA / "investment grade" | The seller's own top tier | Written definition; independent report |
| "D Block" | Rough from Block D of the Merelani mining area | Evidence of origin, since the term is widely borrowed |
Four questions that separate a real grade from marketing
Ask for the hue described in plain words, for example "blue with a violet secondary". Ask for the tone as a proportion, for example "medium, around 65 per cent". Ask whether grey is present at all. Finally, ask for a video in daylight with no filter. A seller who grades honestly will answer all four without hesitation — and when you compare two stones, our price guide tells you what the difference should cost.
Frequently asked questions
Is there an official tanzanite grading system?
No. Unlike diamond colour, tanzanite has no universal scale. Laboratories describe hue, tone and saturation; letter grades such as AAA are trade labels defined by whoever is selling.
Is blue or violet tanzanite more valuable?
Blue with a violet secondary is the most valuable. Stones that read predominantly violet usually sell for less, which makes them strong value for the colour you get.
What does "D Block tanzanite" mean?
It refers to rough from Block D of the Merelani mining area, associated with good blue material. The phrase is used loosely in listings, so treat it as a claim that needs evidence.
Why does my tanzanite look different indoors?
Two reasons: strong pleochroism, so the colour changes with viewing direction, and lighting. Incandescent and jewellery-shop lighting push the stone towards violet and hide grey.
Stones currently available
Each one graded, measured and listed individually.
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