Opal
JewelryWiki Editorial·4 sources·Reviewed 2026-07-31
GIA names opal explicitly as a gem to protect from blows. Suited to earrings and necklaces; a ring or bracelet should be occasional wear.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 5½–6½ [2] | — |
| Toughness | Low. GIA groups opal with tanzanite as "not-so-tough" gems that should be protected from accidental blows. [1] | — |
| Refractive index | 1.370–1.520 [2] | — |
| Crystal system | Amorphous [4] | — |
| Suitability for daily wear | Not recommended for daily rings or bracelets. GIA advises earrings or necklaces, where there is less risk of striking a hard surface, and reserving ring or bracelet settings for special occasions. [1] | — |
| Birthstone month | October — shares October with tourmaline. [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)