Topaz
JewelryWiki Editorial·7 sources·Reviewed 2026-08-04
Hard enough on paper, but perfect cleavage and light sensitivity work against it.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 8 [2] | — |
| Stability | Can fade or change colour from prolonged exposure to light — GIA lists topaz alongside tanzanite and kunzite. [1] | — |
| Refractive index | 1.609–1.643 [2] | — |
| Specific gravity | 3.49–3.57 [2] | — |
| Chemical formula | Al2SiO4(F,OH)2 [7] | — |
| Crystal system | Orthorhombic [4] | — |
| Common treatments | Irradiation is EXTREMELY FREQUENT — GIA’s own emphasis. Colourless topaz has little commercial value, but irradiation followed by heating produces the strong blues that dominate the market, and because strong blue does not occur naturally in topaz, such stones are considered to have been irradiated. Heating alone removes the yellowish component from yellowish-pink topaz to intensify the pink. Topaz is also coated with metal oxides to produce metallic colours not found in nature. [6] | — |
| Care cautions | NEVER use an ultrasonic cleaner — GIA names this among the gems susceptible to heat and temperature change, which should be kept out of an ultrasonic REGARDLESS of whether they have been treated. Use warm soapy water or a solution formulated for delicate gems. [5] | — |
| Birthstone month | November — shares November with citrine. [3] | — |
Sources
- GIA — More than the Mohs Scale: Understanding Gem Durability — Gemological Institute of America (GIA 4Cs, "More than the Mohs Scale" (14 March 2016))
- International Gem Society — reference charts (Mohs hardness, specific gravity, refractive index) — International Gem Society (IGS reference charts)
- Jewelers of America — Birthstones — Jewelers of America (Jewelers of America, Birthstones)
- Wikipedia — mineral article infoboxes (crystal system) — Wikipedia contributors (Wikipedia mineral infoboxes)
- GIA — Ultrasonic Cleaners for Gems: What You Need to Know — Gemological Institute of America (GIA 4Cs, Ultrasonic Cleaners for Gems)
- GIA — An Introduction to Gem Treatments — Gemological Institute of America (GIA, An Introduction to Gem Treatments (Robert Weldon))
- Handbook of Mineralogy — Mineral Data Publishing / Mineralogical Society of America (Handbook of Mineralogy, Mineral Data Publishing)