Amethyst
QuartzJewelryWiki Editorial·5 sources·Reviewed 2026-08-04
The purple variety of quartz, and the most common gem at hardness 7 — the traditional threshold for everyday wear.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 7 [1] | — |
| Chemical formula | SiO2 Read from the species entry, Quartz. A variety shares its species’ formula — unlike hardness or density, which vary with composition and are not inherited here. [5] | — |
| Crystal system | Trigonal [3] Read from the species article, Quartz. | — |
| Common treatments | Heating removes unwanted brownish inclusions and lightens overly dark stones. The relationship runs the other way too: GIA records that varieties of quartz may be irradiated to produce amethyst, and that some amethyst is heated to become citrine. Heat treatment is considered durable and permanent under normal handling. [4] | — |
| Birthstone month | February [2] | — |
Sources
- 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 — 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)