The group
Zoisite was described in 1805 and stayed a collector's curiosity for over a century and a half. Then in 1967 the blue variety was found in the Merelani Hills, Tiffany named it tanzanite, and one variety carried the whole species into the gem trade.
The species is strongly pleochroic, and in tanzanite this is the central fact: the crystal shows blue, violet and, before heating, a brownish red along its three axes. Gentle heat removes the brown and is applied to essentially all of it. The change is permanent — and, importantly, undetectable, so no laboratory report will tell you whether a tanzanite has been heated.
Thulite is the pink, manganese-bearing variety from Norway, cut as cabochons and carved. Anyolite — green zoisite shot through with opaque ruby crystals — is a Tanzanian ornamental rock used for carving rather than faceting.
Across the species, perfect cleavage in one direction is the practical limit. Zoisite is a pendant and earring material first, and a ring stone only in a protective setting.
Every zoisite compared
The whole group side by side. Where the constants overlap, the species cannot be named from a refractometer alone — which is exactly why the trade names mislead.
| Variety | Species | Colour | Mohs | RI | SG | Guide price |
|---|---|---|---|---|---|---|
| Anyolite | A metamorphic rock: green zoisite with pink-red corundum crystals and black pargasite amphibole | green | 6-7 zoisite, 9 corundum - an awkward hardness contrast for polishing | 1.69-1.70 (zoisite), 1.76-1.77 (corundum) | 3.00-3.40 | $3-20 per kilogram rough; carved figures and spheres $30-500 |
| Clinozoisite | Clinozoisite | green | 6–7 | 1.706–1.735 | 3.21–3.38 | $10–120/ct |
| Green Zoisite | Zoisite | green | 6–6.5 | 1.690–1.700 (spot ~1.70) | 3.20–3.40 | $0.50–10/ct; sculptures priced by workmanship |
| Tanzanite | Zoisite | blue | 6–7 | 1.691–1.700 | 3.10–3.38 | $80–1,200/ct |
| Thulite | Zoisite | pink | 6–6.5 | 1.690–1.700 (spot ~1.70) | 3.10–3.40 | $0.50–10/ct |
| Zoisite | Zoisite | green | 6–7 | 1.685–1.707 | 3.20–3.50 | Massive material 1–10 USD per kg; gem tanzanite 200–1,500 USD/ct |
Questions
Is tanzanite the same as zoisite?
Tanzanite is the blue-violet gem variety of the mineral zoisite. All tanzanite is zoisite; most zoisite is not tanzanite.
Can a laboratory tell whether tanzanite is heated?
No. Heating in tanzanite is not detectable by standard gemmological testing, and the major laboratories do not state heated or unheated on a routine tanzanite report. A premium charged for "unheated" tanzanite is a premium for something nobody can verify.
What is anyolite?
Green zoisite containing opaque ruby crystals, from Longido in Tanzania. It is an ornamental rock used for carving and decorative objects, not a faceting material.
Looking for zoisite?
Tell us which variety, what size and what it is for. We source it, photograph it and quote it, with the locality named.
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