ELMONAS / EDUCATION
Lab-grown diamond vs moissanite vs cubic zirconia
The short answer
A lab-grown diamond is diamond; moissanite and cubic zirconia are simulants, different materials that only resemble diamond.
What is the short answer?
A lab-grown diamond is diamond. Moissanite and cubic zirconia are simulants: different materials that resemble diamond but are not diamond. The three differ measurably in hardness, optical behaviour and density.
How do the three materials compare?
| Property | Lab-grown diamond | Moissanite | Cubic zirconia (CZ) |
|---|---|---|---|
| Material | Carbon crystal | Silicon carbide | Zirconium dioxide |
| Is it diamond? | Yes | No | No |
| Mohs hardness | 10 | About 9.25 | About 8 to 8.5 |
| Refractive index | 2.42 | 2.65 to 2.69 | 2.15 to 2.18 |
| Dispersion (fire) | 0.044 | 0.104 | About 0.058 to 0.066 |
| Specific gravity | 3.52 | About 3.2 | About 5.6 to 6.0 |
| Optical character | Singly refractive | Doubly refractive | Singly refractive |
In practice: moissanite has higher dispersion than diamond, which shows as stronger rainbow flashes; CZ is much denser, so it weighs more than a diamond of the same size, and it is softer than diamond.
Can a diamond tester tell them apart?
Partly. Thermal testers separate diamond from cubic zirconia, but the US Federal Trade Commission cautions that moissanite can falsely register as diamond on a thermal tester. A newer tester, or a gemological laboratory, separates moissanite from diamond.
A lab-grown diamond will read as diamond on a thermal tester, because it is diamond.
Are moissanite and CZ bad products?
No. GIA notes that a simulant can be a reasonable purchase when it is an informed decision. The issue is disclosure: simulants are not diamond and should be described as simulants or imitations.
The FTC's Jewelry Guides say sellers of imitation diamonds should describe them as "imitation" or "simulated" immediately before the word "diamond", and sellers of laboratory-created diamonds should describe them as "laboratory-grown" or "laboratory-created" immediately before the word "diamond".
What does Elmonas sell?
Elmonas sells lab-grown diamonds only. Every stone is a lab-grown diamond with an IGI or GIA report.
Sources
- GIA 4Cs, Simulants, Moissanite and Lab-Grown Diamonds (simulants vs lab-grown diamonds): https://4cs.gia.edu/en-us/simulants-moissanite-and-lab-grown-diamonds/
- Federal Trade Commission, In the Loupe: Advertising Diamonds, Gemstones and Pearls (disclosure rules, moissanite and thermal testers): https://www.ftc.gov/business-guidance/resources/loupe-advertising-diamond-gemstones-pearls
- GIA, An Introduction to Simulants or Imitation Gem Materials (CZ and moissanite hardness, fire and appearance): https://www.gia.edu/gem-imitation
- Gems & Gemology, Winter 1997, Synthetic Moissanite: A New Diamond Substitute (moissanite optical and physical properties): https://www.gia.edu/gems-gemology/winter-1997-synthetic-moissanite-nassau0
- Gems & Gemology, Spring 1980, Cubic Zirconia: an Update (CZ refractive index, dispersion, hardness, specific gravity): https://www.gia.edu/dam/migrated-assets/docs/doc1/Cubic-Zirconia.pdf
- International Gem Society, Properties of Diamond Simulants (diamond refractive index, dispersion, specific gravity, hardness; moissanite and CZ for comparison): https://www.gemsociety.org/article/diamond-and-simulant-comparison-chart/
Last reviewed: 18 October 2026
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