Diamond
DiamondJewelryWiki Editorial·7 sources·Reviewed 2026-08-04
The hardest gemstone, and routinely assumed to be indestructible. GIA is explicit that it is not: diamonds resist scratching, but a hard blow can cleave or fracture one.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 10 — the hardest gemstone [1] | — |
| Toughness | Not the toughest despite being the hardest. GIA: while they resist scratching and abrasions, diamonds can be cleaved or fractured by a hard blow. [1] The single clearest demonstration that hardness and toughness are different properties. | — |
| Refractive index | 2.417–2.419 [2] | — |
| Specific gravity | 3.50–3.53 [2] | — |
| Chemical formula | C [7] | — |
| Crystal system | Cubic [4] | — |
| Common treatments | Four distinct treatments. Surface-reaching fractures are filled with high-lead-content glass — the fracture is still there, just less apparent. HPHT (high pressure, high temperature) removes or changes colour and is difficult to identify even for seasoned gemmologists. Irradiation, often followed by heating, induces black, green, blue-green, deep yellow, orange, pink and red. Laser drilling burns a channel to reach a dark inclusion, which is then chemically bleached. Filling is often encountered; irradiation is frequent in fancy colours. [6] | — |
| Suitability for daily wear | Excellent for daily wear on the hardness axis. Chipping remains possible at the girdle from a hard knock, which a protective setting mitigates. [1] | — |
| Care cautions | Generally ultrasonic-safe, with one exception GIA is explicit about: a FRACTURE-FILLED diamond must not go in an ultrasonic. The filling is a lead-glass-like substance, it is not permanent, and GIA illustrates the point with a 0.34 ct treated diamond damaged exactly that way. [5] | — |
| Birthstone month | April [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)