Moissanite vs Diamond: How to Tell the Difference

Diamond is pure carbon, the hardest natural material at 10 on the Mohs scale, and singly refractive. Moissanite is silicon carbide, made in laboratories for jewellery since 1998, slightly softer at about 9.25, doubly refractive and more than twice as dispersive, so it throws stronger rainbow flashes than a diamond.

Look through the side of the stone with a 10x loupe: moissanite is doubly refractive, so the back facet edges look doubled, while a diamond's look single. Moissanite also shows stronger rainbow fire and is slightly lighter for its size. A moissanite tester or a gemmologist settles any doubt in seconds.

A basic thermal diamond tester will not. Moissanite carries heat almost as well as diamond, so a thermal probe reads it as diamond, which GIA reported when moissanite first appeared in 1997. A combined tester that also measures electrical conductivity separates the two, because moissanite conducts electricity and most diamonds do not.

Moissanite is a real gemstone in its own right, silicon carbide, but it is not diamond. Sold honestly as moissanite it is a diamond alternative; sold as diamond it is a misdescription. Natural moissanite is extremely rare, so the stones in jewellery are made in laboratories.

No. A lab-grown diamond is diamond: carbon with the same chemical, physical and optical properties as a mined diamond. Moissanite is a different material, silicon carbide, with its own hardness, brilliance and double refraction. A gemmologist can separate moissanite from any diamond; separating lab-grown from mined diamond needs a laboratory.

Only if the stone has been replaced. Gem moissanite reached jewellers in 1998, so a Victorian, Edwardian or Art Deco ring set with moissanite has had a stone changed in recent years. Moissanite is now also cut in old mine and old European styles, so an old-looking cut does not prove an old diamond.

Moissanite is very hard, about 9.25 on the Mohs scale, so it resists scratching in daily wear and does not go cloudy. Like a diamond, it can look dull when grease builds up on the back facets, and warm soapy water with a soft brush restores it. Only diamond is harder.

A diamond ring is valued on the diamond's cut, colour, clarity and carat weight, any laboratory certificate, the metal and setting, and the maker. Antique cuts and signed pieces can be worth more than the stones alone. We first confirm the stone is diamond, not moissanite or another simulant, then value it free from photographs.

Natural moissanite occurs only in tiny grains, first found in rock from the Canyon Diablo meteorite crater in Arizona and later in a few other rocks. The grains are far too small and rare to cut as gems, so every moissanite sold in jewellery is laboratory made, not natural.

Moissanite rings are sold mainly by online jewellers and some high street shops. Whoever you buy from, check the listing names the stone as moissanite, states the metal and its hallmark, and gives the stone's size in millimetres. Mozeris sells antique and vintage diamond and gemstone rings rather than moissanite.

Check the colour, since older moissanite can look slightly green or yellow and newer stones are near colourless; the cut, which decides how much it sparkles; the metal and its hallmark; and whether the setting holds the stone securely. Ask for the stone's size in millimetres and the seller's returns terms.

VVS is a clarity term borrowed from diamond grading, meaning very very slightly included. On moissanite it is a seller's description, because GIA does not grade moissanite on its diamond scales. GRA reports come with many moissanite pieces sold online; they are not reports from the major gem laboratories.

Yes. Moissanite varies in colour, from near colourless to faintly green, yellow or grey, and in clarity and cutting quality, which affect how it looks. Sellers grade these themselves, often using diamond terms. It is also made in coloured versions and cut in modern and old styles, including old European cuts.

Moissanite is manufactured in any quantity, so on the second-hand market a moissanite ring is usually valued on its gold or platinum and any maker rather than the stone. We buy gold and platinum jewellery: send photographs and the hallmark for a free valuation within one working day.

Moissanite is hard, about 9.25 on the Mohs scale, so it wears well every day, and it is very brilliant. It is not diamond, and it shows stronger rainbow flashes than a diamond, which some people prefer and others do not. Buy it described clearly as moissanite, with a hallmarked gold or platinum mount.

Moissanite has a higher refractive index than diamond and more than twice its dispersion, so it returns more light and throws stronger rainbow flashes, especially in sunlight and in larger stones. A well cut diamond shows more white brilliance and finer colour. Many people can tell the two apart by that fire alone.

Yes. Moissanite is hard and stable and is not harmed by water, so you can wear it every day. Soap and lotion leave a film on the back of the stone that dulls it, so take it off to wash, swim in chlorinated water or apply creams. The metal setting needs the same care as any ring.

Warm water, mild washing-up liquid and a soft toothbrush clean moissanite best: brush behind the stone, rinse and dry with a lint-free cloth. Mild solutions do not harm the stone itself, but acids such as vinegar can dull some metals and other gemstones in the same piece, so soapy water is safer.

Yes. Laboratory-made moissanite often contains fine needle-like inclusions or stringers, and because the stone is doubly refractive these look doubled under a loupe, which helps tell moissanite from diamond. Better stones show few inclusions, and many look clean to the naked eye.

A Portuguese cut is a round cut with extra rows of facets on the crown and the pavilion, giving a dense, glittering pattern of small flashes rather than the larger flashes of a round brilliant. It is used for moissanite and for coloured gemstones, and it takes longer to cut than a standard brilliant.

Moissanite can be weighed in carats like any gem, but it is lighter than diamond, so a moissanite the same size as a 1 ct diamond weighs less. Sellers therefore often describe moissanite by its size in millimetres or as a diamond-equivalent weight. Compare stones by millimetre size rather than carats.

Moissanite sinks, like diamond, because it is far denser than water, with a specific gravity of about 3.22 against diamond's 3.52. Floating tests do not separate gems. A loupe showing doubled facet edges, or a multi tester, is the reliable way to tell moissanite from diamond.