Smoky quartz
QuartzJewelryWiki Editorial·2 sources·Reviewed 2026-08-04
Brown to nearly black transparent quartz. Its colour comes from natural irradiation acting on traces of aluminium in the crystal — and the same effect is produced commercially, so a great deal of the very dark material on the market was irradiated in a laboratory rather than underground.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 7 [1] | — |
| Specific gravity | 2.651 [2] | — |
| Chemical formula | SiO2 Read from the species entry, Quartz. A variety shares its species’ formula. [2] | — |
| Crystal system | Hexagonal [2] | — |
| Common treatments | Commonly irradiated. GIA records that varieties of quartz are irradiated, and that irradiated quartz colours are stable provided they are not exposed to high temperatures. Very dark, uniform smoky quartz is the usual sign. [1] | — |
| Care cautions | Stable in normal wear, but heat can drive off the colour — tell a jeweller before any repair involving a torch. [1] | — |
Sources
- International Gem Society — gemstone articles — International Gem Society (IGS, gemstone information articles (gemsociety.org))
- Handbook of Mineralogy — Mineral Data Publishing / Mineralogical Society of America (Handbook of Mineralogy, Mineral Data Publishing)