Moissanite

Moissanite is the mineral name for silicon carbide. It is named after the French chemist Henri Moissan, who found crystals of it in the Canyon Diablo meteorite in Arizona. In nature it occurs only as tiny green-to-black crystals, too small to cut into a gem in practice, so the moissanite in jewellery is grown in a laboratory. Lab-grown moissanite gems were first marketed in 1998.

It helps to keep three materials apart. A natural diamond formed in the earth. A lab-grown diamond is real diamond made in a laboratory, with the same crystal structure and nearly the same properties. Moissanite is what GIA calls a simulant: a material made of different atoms that only looks similar. That difference matters when you read a grading report, because a diamond grading report describes a diamond. If a moissanite comes with a "grade", ask who issued it and which scale it uses.

Moissanite is the closest to diamond of the common look-alikes. The figures below come from Kurt Nassau's 2000 paper on the stones that had reached the market two years earlier. The higher dispersion is what you see as stronger rainbow flashes. Some people love that livelier look, and some find it busier than the more neutral sparkle of a diamond cut to a good grade. That is a matter of taste, so compare both under daylight and indoor light before you decide.

Two more differences are practical. Moissanite is lighter for its size (specific gravity 3.22 against 3.52 for diamond), so a stone of the same weight is slightly bigger across, which is why moissanite is usually described by millimetre size as well as by carat weight. And it is a little softer: 9¼ on the Mohs scale against diamond's 10.

Not by eye, and not with a basic thermal tester. Moissanite conducts heat so much like diamond that all the thermal probe testers Nassau tried gave a "diamond" reading. A thermal tester separates both from other look-alikes, but it cannot separate them from each other. Testers made specifically for moissanite exist; Nassau describes one that works from ultraviolet absorption and is used after the thermal test.

A trained gemmologist looks for double refraction. Diamond bends light as a single beam, while moissanite splits it in two, so under magnification the facet edges can look doubled. Moissanite is cut with its optic axis perpendicular to the table, so a view straight down can hide the effect and you need to look at an angle. Other clues are white needle-like inclusions, polishing lines that all run one way, and slightly rounded facet edges. Laboratories confirm identity with infrared or Raman spectroscopy.

If a stone carries a laser inscription, match it to a report issued by the lab. GIA's journal has recorded a 1.02 ct round stone with a fraudulent GIA inscription that proved to be synthetic moissanite, so an inscription on its own is not proof.

For daily wear, yes, with limits. Diamond is still the harder stone. Moissanite has no strong cleavage plane, which led Nassau to conclude that it is tougher than diamond against chipping. It also copes well with the heat a jeweller uses: he reports excellent resistance to soldering and to the usual setting, repair and cleaning work, and stability in air to 1700°C (3092°F). In practice that means a moissanite ring can be resized and repaired, though you should tell the jeweller what the stone is first.

Colour deserves a look. The stones marketed in 2000 ranged from J to M on the diamond colour scale, some with grey, green, yellow or brown tints, though the strong fire tended to make them look whiter than a diamond of the same grade. That is a snapshot from 2000 and from one maker's stones, so judge the stone you are actually buying, in the setting you chose, rather than relying on an old figure.

Plainly, under its own name. In the United States, the FTC's Jewelry Guides say a gemstone name used for a laboratory-made stone should be preceded by a qualifier such as "laboratory-grown", and that the word "diamond" is reserved for a mineral of essentially pure carbon, so moissanite should never be described as a diamond. Those are US guidelines, not binding law, but the principle is a good test of any listing in Canada too.

Ask for the stone's name, its size in millimetres and its weight in carats in writing. If a seller quotes a "diamond equivalent" weight, ask what it means. Moissanite is one of the three stone choices on the custom engagement rings page, next to natural and lab-grown diamonds, and you can shape the ring in the design studio or look at samples in a showroom.