Two different materials
A lab-grown diamond is diamond: pure carbon in a cubic crystal, grown in a laboratory instead of mined. It is the same material as a diamond from the earth.
Moissanite is silicon carbide. The chemist Henri Moissan first found it in 1893, in rock from a meteorite crater in Arizona. Natural moissanite is far too rare to cut, so every moissanite in jewelry is made in a laboratory.
Moissanite is a gem in its own right. It is also the most convincing diamond simulant, a different material that resembles diamond, which is why the two are so often compared.
Side by side
| Property | Lab-grown diamond | Moissanite |
|---|---|---|
| Material | Carbon | Silicon carbide |
| Is it diamond | Yes | No |
| Hardness, Mohs | 10 | 9.25 |
| Refractive index | 2.42 | 2.65 to 2.69 |
| Dispersion, or fire | 0.044 | 0.104 |
| Refraction | Single | Double |
| Density | 3.52 grams per cubic centimetre | 3.21 grams per cubic centimetre |
| Graded on the four Cs | Yes | No |
How they look
Fire. Moissanite has more than twice the dispersion of diamond, so it breaks light into more coloured flashes. In sunlight a moissanite throws rainbows that a diamond does not. Some people love the effect. Others find that it gives the stone away, most of all above one carat.
Doubling. Moissanite bends light along two paths. Seen at an angle under magnification, the facet edges at the back of the stone appear doubled. In a diamond they never do. It is the quickest way a jeweler tells the two apart.
Colour. Diamonds are graded for colour from D to Z. Modern moissanite is near colourless, though some stones show a faint yellow, green or grey tint in certain light.
How they wear
Both are hard enough to wear every day. Diamond is 10 on the Mohs scale, the hardest material known. Moissanite is 9.25, harder than sapphire and ruby.
The Mohs scale is a ranking, not a ruler. The step from 9 to 10 is far larger than any step below it, so over the decades a diamond keeps sharper facet edges than any other gem.
How to tell them apart
A basic diamond tester measures how quickly a stone carries heat away. Moissanite carries heat nearly as well as diamond, so it can pass that test. Testers made for the purpose add an electrical test, because moissanite conducts electricity and most diamonds do not.
Weight is another clue. Moissanite is about a tenth lighter than diamond, which is why it is usually sold by its size in millimetres and not by carat weight.
A diamond with a grading report settles the question. The report states what the stone is, and its number is inscribed on the girdle.
Price, and which to choose
Moissanite costs less than a lab-grown diamond of the same size. A lab-grown diamond in turn costs considerably less than a mined one.
- Choose moissanite if price matters most and you like its extra fire.
- Choose a lab-grown diamond if you want a diamond: the material, the look and the grading report that goes with it.
ART sets lab-grown diamonds only. Read how they compare with mined stones in lab-grown and natural diamonds compared.
