Key facts
| Stone | What it is | Mohs hardness | Refractive index | Dispersion (fire) | How it is grown |
|---|---|---|---|---|---|
| Lab diamond | Carbon | 10 | 2.42 | 0.044 | HPHT or CVD |
| Moissanite | Silicon carbide | 9.25 | 2.65 to 2.69 | 0.104 | Seeded sublimation growth |
| Lab sapphire / ruby | Corundum, aluminium oxide | 9 | 1.76 to 1.77 | 0.018 | Flame fusion, flux, hydrothermal, Czochralski |
| Lab emerald | Beryl | 7.5 to 8 | 1.57 to 1.58 | 0.014 | Hydrothermal or flux |
| Cubic zirconia | Zirconium oxide (simulant) | 8 to 8.5 | 2.15 to 2.18 | 0.060 | Skull melting |
| Glass | Silica (simulant) | 5 to 6 | about 1.5 | varies | Melted |
Standard gemological reference values. Dispersion is the spread between red and violet refractive indices; higher means more rainbow flash.
Grading letters
- Colour D to Z: D is colourless; G to H is near-colourless and where most diamond jewellery sits; the scale is for diamond and is borrowed for moissanite.
- Clarity FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1 to I3: FL flawless down to I3 included; VVS means very, very slightly included at 10x.
- Cut Excellent / 3EX: GIA's top cut grade; 3EX means Excellent for cut, polish and symmetry.
- Carat: 0.2 grams. Melee is roughly under 0.2 carat and is sold by millimetre diameter; a 1mm round is about 0.005 carat, a 3mm round about 0.1 carat.
- Reports: GIA and IGI grade individual stones and inscribe the girdle; GRA is a private moissanite report; "certificate" without a lab name means nothing.