Key facts

ReferenceUpdated November 1, 2026

Illustration (AI render): moissanite, lab sapphire, lab ruby, lab emerald and lab diamond.

The Mohs hardness scale from 1 to 10: talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, diamond. Each scratches the ones below it. — Illustration made with AI; the facts are ours and checked.

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		9.25	2.65 to 2.69	0.104	Seeded sublimation growth
Lab sapphire / ruby	, aluminium oxide	9	1.76 to 1.77	0.018	Flame fusion, flux, hydrothermal, Czochralski
Lab emerald		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 to F is colourless; G to J is near-colourless (GIA's range) 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 examine individual stones. Lab-grown diamonds they grade are laser-inscribed with the report number; natural diamonds often are too, but at GIA the inscription is optional and costs extra. Since 1 October 2025 GIA no longer grades lab-grown diamonds on the D-to-Z colour and FL-to-I3 clarity scales: it gives a "Premium" or "Standard" designation, or no assessment below Standard (GIA, 26 August 2025; GIA, 2 June 2025). IGI still gives full grades. A GRA card, which comes with most moissanite, is a seller-supplied card, not a report from an independent laboratory; "certificate" without a lab name means nothing.

Prices

What lab-grown and mined loose stones cost per carat, gem by gem, worked out from each day’s listing prices: lab vs mined gem prices. For the growth methods behind the table above, see how lab gems are grown.