Mineral · Nesosilicates
Topaz
Al2(SiO4)(F,OH)2
Topaz is aluminium fluorosilicate, hardness 8, forming prismatic crystals in pegmatites and rhyolites: sherry-coloured Topaz Mountain (Utah, state gem), imperial topaz from Ouro Preto (Brazil), giant colourless crystals from Minas Gerais and Ukraine, and blue and pink crystals from Pakistan (Katlang). Perfect basal cleavage means crystals often show a flat cleavage base. Utah topaz fades from sherry to colourless in sunlight.
| Formula | Al2(SiO4)(F,OH)2 |
|---|---|
| IMA status | grandfathered |
| Crystal system | Orthorhombic |
| Mohs hardness | 8 |
| Group | Nesosilicates |
| Type locality | None (known since antiquity) |
| Streak | White |
| Specific gravity | 3.5 |
| Reference list | IMA List of Minerals (RRUFF) — verify formula and status against the current list |
Fakes and treatments
Nearly all blue topaz in jewellery is irradiated colourless topaz; 'mystic topaz' is coated. Specimen crystals are rarely treated.
Elsewhere
Cite this article
Stratum Study. "Topaz" (Mineral). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/minerals/topaz. Accessed 2026-09-20.
@misc{stratum-topaz,
title = {Topaz},
author = {{Stratum Study}},
howpublished = {\url{https://stratum.black/study/minerals/topaz}},
year = {2026},
note = {Mineral article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, wikidata, commons. 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.