Ruby
CorundumJewelryWiki Editorial·7 sources·Reviewed 2026-08-04
Ruby and sapphire are the same mineral — corundum — and share its hardness and excellent toughness. Among the best choices for a ring worn every day.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 9 [1] | — |
| Toughness | Excellent. [1] | — |
| Specific gravity | 3.97–4.05 [2] | — |
| Chemical formula | Al2O3 Read from the species entry, Corundum. A variety shares its species’ formula — unlike hardness or density, which vary with composition and are not inherited here. [7] | — |
| Crystal system | Trigonal [4] Read from the species article, Corundum. | — |
| Common treatments | Heavily treated as a species, by three separate methods. Heating removes purplish colour to render a purer red and removes “silk” — minute needle-like inclusions that make a stone look lighter and more opaque — or, conversely, recrystallises the silk to strengthen a star. Surface-reaching fractures are filled with glass to make the stone more transparent than it really is, and GIA notes the amount of filler can be significant. Lattice diffusion of beryllium can accentuate the colour. Filling is often encountered in the trade; diffusion-treated corundum is widespread. [6] | — |
| Suitability for daily wear | Excellent. High on both axes that matter, which is why corundum is the standard recommendation for daily-wear coloured stones. [1] | — |
| Care cautions | Transparent ruby requires caution in an ultrasonic; STAR ruby should not be cleaned in one at all. Avoid ultrasonics on any stone that has been heat-treated to enhance colour. [5] | — |
| Birthstone month | July [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)