Moissanite is silicon carbide. Gem quality stones have a Mohs hardness of about 9.25, a refractive index of about 2.65 to 2.69, a dispersion of 0.104 and a specific gravity of about 3.22. Diamond is harder (Mohs 10) but has a lower refractive index (2.42) and a lower dispersion (0.044). The full table is below.
The specification table
Figures for gem quality synthetic moissanite come from the Gems & Gemology study of the material (Nassau, Winter 1997). Diamond figures come from standard reference data. Published values vary slightly between sources, so where they do we say so.
| Property | Moissanite | Diamond |
|---|---|---|
| Chemical composition | Silicon carbide (SiC) | Carbon (C) |
| Mohs hardness | About 9.25 | 10 |
| Refractive index | 2.648 to 2.691 | 2.418 |
| Birefringence | About 0.043 (doubly refractive) | None (singly refractive) |
| Dispersion | 0.104 | 0.044 |
| Specific gravity | About 3.22 | About 3.52 |
| Crystal system | Hexagonal | Cubic |
Sources: Gems & Gemology, Winter 1997, Synthetic Moissanite, Wikipedia, Moissanite and Wikipedia, Diamond, checked 10 October 2026.
Hardness: how well it resists scratching
Moissanite sits at about 9.25 on the Mohs scale. Only diamond is harder, and in practice that makes moissanite hard enough for every day wear. It is far harder than cubic zirconia, glass or the grit in household dust.
Mineral reference data sometimes lists moissanite at 9.5, and others give a range of 9 to 9.5. The gem trade figure is 9.25, and that is the one we use. Diamond is harder, and we say so plainly. Mohs is also a ranking, not an even scale, so the gap between 9.25 and 10 is not a small step.
Refractive index: how strongly it bends light
Refractive index measures how much light slows and bends on entering a stone. A higher number generally means more light is turned back out through the top. Moissanite measures 2.65 on average (2.648 to 2.691 depending on direction), against 2.42 for diamond.
That is a statement about the material, not a promise about how any one stone looks. Cut quality, size and lighting decide that. This is also why we do not put a percentage on brilliance. The honest comparison is the two numbers.
Dispersion: where the rainbow flashes come from
Dispersion is how widely a stone splits white light into spectral colours. Moissanite is 0.104 and diamond is 0.044. This is the property behind the coloured flashes people notice in moissanite. It is about colour, not about how bright the stone is. Some people love the extra fire. Others prefer the quieter, whiter flash of a diamond. Both are matters of taste.
Density: why size is quoted in millimetres
Moissanite has a specific gravity of about 3.22 and diamond about 3.52. A moissanite therefore weighs less than a diamond of the same dimensions. That is why a carat weight on its own is a poor guide to the size of a moissanite, and why we list stone diameter in millimetres next to carats. Our Eterna ring, for example, lists 1 carat as 6.5 mm, 2 carat as 8 mm and 3 carat as 9.1 mm.
Optical character and the diamond tester
Moissanite is doubly refractive, which means a ray of light entering the stone splits in two. Under magnification this shows as a doubling of the facet edges, and it is one way a gemmologist can tell moissanite from diamond. Its thermal behaviour, though, is close enough to diamond that common thermal testers read it as diamond. Our guide to whether moissanite passes a diamond tester covers what that means in practice.
One more reference figure: moissanite does not melt in the ordinary way. Reference data gives a decomposition temperature of about 2,730 degrees Celsius, far beyond anything a jewellery repair or house fire would raise.
What these numbers do not tell you
A specification table describes a material. It does not describe a ring. The metal, the plating, the cut and the workmanship matter as much. Mariqe is an Australian company, ECOM CULTURE PTY LTD. Our stones are cut and pieces assembled overseas. Each piece includes a GRA report and a unique certification code, which is a record of the stone and not an independent valuation, as our GRA certificate guide explains. The settings are 925 sterling silver with platinum or 18k gold plating, and plated jewellery needs the normal care any plated piece does.
Moissanite is lab grown, not mined, and conflict free. Natural crystals are too small and rare to cut, which our article on where moissanite comes from explains.
What this means for you
If durability matters most, moissanite is hard enough for daily wear and diamond is harder still. If you like fire and colour in the light, moissanite's dispersion is more than double diamond's. If you are comparing sizes, compare millimetres, not carats. The stone figures above are fixed properties of the material, so you can check them against any seller's claims.
Eterna Ring
A six-prong round lab grown moissanite solitaire in 925 sterling silver with platinum or 18k gold plating, from $79 for 1 carat in silver (checked 10 October 2026, the product page is final), backed by the Lifetime Moissanite Warranty.
See sizes and pricesFrequently asked questions
How hard is moissanite compared with diamond?
Moissanite is about 9.25 on the Mohs scale and diamond is 10. Diamond is harder, but moissanite is hard enough for daily wear.
What is the refractive index of moissanite?
Gem quality moissanite measures 2.648 to 2.691, commonly quoted as 2.65. Diamond is 2.42.
What is moissanite's dispersion?
Moissanite's dispersion is 0.104, compared with 0.044 for diamond. Dispersion describes how much a stone splits white light into coloured flashes.
Does moissanite weigh less than diamond?
Yes. Moissanite has a specific gravity of about 3.22 and diamond about 3.52, so a moissanite of the same size weighs less. Compare stone diameter in millimetres rather than carats alone.