Mineral · Epidote group
Zoisite
Ca2Al3(Si2O7)(SiO4)O(OH)
Zoisite is the orthorhombic epidote-group mineral whose blue-violet vanadium variety is tanzanite, found only in the Merelani Hills of Tanzania; thulite is the pink manganese variety from Norway and anyolite is the green zoisite with ruby from Longido, Tanzania. Tanzanite crystals on matrix are expensive collector pieces. Nearly all cut tanzanite is heated from brown to blue.
| Formula | Ca2Al3(Si2O7)(SiO4)O(OH) |
|---|---|
| IMA status | grandfathered |
| Crystal system | Orthorhombic |
| Mohs hardness | 6–7 |
| Group | Epidote group |
| Type locality | Saualpe, Carinthia, Austria |
| Streak | White |
| Specific gravity | 3.3 |
| Reference list | IMA List of Minerals (RRUFF) — verify formula and status against the current list |
Fakes and treatments
Heat treatment of tanzanite is universal and accepted but should be stated; synthetic forsterite and glass imitate it. Tanzania restricts export of rough tanzanite over 1 gram to licensed dealers.
Elsewhere
Cite this article
Stratum Study. "Zoisite" (Mineral). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/minerals/zoisite. Accessed 2026-09-20.
@misc{stratum-zoisite,
title = {Zoisite},
author = {{Stratum Study}},
howpublished = {\url{https://stratum.black/study/minerals/zoisite}},
year = {2026},
note = {Mineral article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, wikidata. Accessed 2026-09-20.}
} Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.