Key properties
| Chemical formula | C |
| Crystal system | Cubic |
| Mohs hardness | 10 |
| Toughness | Good to exceptional (good along cleavage directions, exceptional elsewhere) |
| Refractive index | 2.417 |
| Optic character | Singly refractive |
| Dispersion | 0.0440 |
| Specific gravity | 3.51-3.53 |
| Cleavage | Perfect in four directions (octahedral {111}) |
| Fracture | Step-like (irregular to conchoidal along cleavage planes) |
| Habit | Octahedra most common, also dodecahedra, cubes and rounded resorbed forms with triangular etch pits (trigons); twinned macles |
| Lustre | Adamantine; polish: Adamantine |
| UV fluorescence | About a quarter to a third of gem diamonds fluoresce, typically blue in LW and weaker in SW; yellow fluorescence may flag certain treatments or nitrogen types and can slightly affect price |
| Pleochroism | None |
| Cause of colour | Nitrogen centres (yellow to brown), boron (blue, also electrically conducting), natural or laboratory irradiation damage (green), plastic deformation of the lattice (pink, brown, red); pure Type IIa is colourless |
| Typical inclusions | Mineral crystals (garnet, diopside, olivine, enstatite, sulphides), clouds, feathers, included crystals with tension cracks, twinning wisps, needles, naturals and bearding on the girdle, trigons on crystal faces; HPHT-grown synthetics trap metallic flux, CVD shows layered growth striations |
| Stability | Stable to light and chemicals; burns in oxygen above about 700 degrees C — a bench torch will damage it |
| Heat sensitivity | High temperatures will etch or burn the surface; protect during repair work |
| Care and cleaning | Ultrasonic and steam safe unless heavily fractured; warm soapy water with a soft brush ideal |
| Birthstones | April; 10th, 60th and 75th anniversaries |
| Availability | Plentiful through the mining and recycling pipeline; natural fancy colours (red, blue, pink, violet) rare to extremely rare |
| Recognition | Universal — the most recognised gemstone; graded by the GIA-created 4Cs (colour, clarity, cut, carat) |
Varieties
Diamond (colourless-near colourless)
| Colour | colourless through light yellow, brown or grey (D to Z) |
| Transparency | transparent |
| Clarity type | Graded Flawless through I3 (Fl, IF, VVS1-2, VS1-2, SI1-2, I1-3) at 10x magnification |
| Phenomena | None |
| Appearance | Brilliant white sparkle from total internal reflection plus dispersion fire; sharp facet junctions and adamantine polish that no simulant fully matches |
| Trade names | river (historic, top colourless) • cape (historic, yellowish) • canary (fancy yellow) • chameleon (rare green that darkens reversibly in darkness) |
| Misnomers | no gem misnomers for diamond itself; beware simulants sold loosely as 'diamonds' — cubic zirconia, moissanite and glass are not diamond |
| Typical sizes | Melee upward; jewellery centre stones typically 0.3 to 3 ct; crystals over 100 ct rare and famous |
| Cutting styles | Round brilliant dominant; princess, oval, cushion, emerald, asscher, pear, marquise, radiant; fancy cuts trade fire for weight retention |
| Key separations | vs cubic zirconia: thermal tester, SG 5.8 vs 3.52, facet junction wear, orange flash; vs synthetic moissanite: moissanite passes diamond thermal testers — use a moissanite-specific tester, look for doubling of facet junctions (DR); vs YAG and GGG: SG and dispersion; vs strontium titanate: extreme dispersion and fragility; vs zircon: strong doubling and lower thermal inertia; vs CVD or HPHT-grown synthetic diamond: fluorescence and phosphorescence patterns, growth striations, metallic inclusions — advanced testing needed |
| Sources (localities) | Botswana (Orapa, Jwaneng) • Russia (Yakutia) • Canada (Diavik, Ekati) • South Africa (Cullinan, Kimberley) • Angola • Namibia (marine) • Zimbabwe • Lesotho (Letseng) • DR Congo • Australia (Argyle, closed 2020, was the pink diamond source) |
| Availability | Steady supply through the pipeline at all commercial grades; large D-IF and fancy colours rare |
| Market notes | The most standardised gem market: GIA and other lab reports set colour, clarity, cut and fluorescence. Lab-grown diamond (HPHT and CVD) now holds a large share of the colourless engagement market at much lower prices — always disclose growth origin |
| Care notes | Ultrasonic and steam usually safe; protect from torch heat and hard knocks along cleavage despite the hardness |
| In short | The colourless diamond of the D-to-Z scale is the archetypal gem — Mohs 10, singly refractive 2.417, and dispersed into fire like nothing natural except its simulants' exaggerations. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 0.30–0.50 | $900.00 – $4000.00 | commercial to fine | 2026-10-26 |
| 0.50–1.00 | $1200.00 – $9000.00 | commercial to fine | 2026-10-26 |
| 1.00–3.00 | $2500.00 – $25000.00 | commercial to top (D-IF, triple excellent) | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #155
Related materials: Corundum · Opal · Quartz · Spinel · Topaz · Tourmaline
Identification wizard · All 83 materials · Singapore gem labs