Moissanite
Last updated: April 2026
All gem-quality moissanite in trade is synthetic silicon carbide (SiC), grown by CVD. Natural moissanite occurs only as microscopic crystals in meteorites and rare terrestrial deposits and is not used as a gemstone. The relevant identification question is moissanite vs. diamond, not natural vs. synthetic moissanite.
Moissanite has a specific gravity of 3.22 and a refractive index of 2.648–2.691, with a Mohs hardness of 9.25. It is uniaxial +.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Key Differentiators
- All commercial moissanite is synthetic — no natural gem exists
- Strongest facet doubling of any gem (birefringence 0.041) — immediately visible under 10× loupe
- Thermal tester falsely reads 'diamond' — always use dedicated moissanite (electrical) tester
- RI 2.648–2.691 — far off the refractometer scale
- LW fluorescence variable — older material often orange/yellow; current near-colorless production is typically weak (unlike typical diamond blue)
Natural vs. Synthetic
Synthetic moissanite is commercially available (CVD — Chemical Vapour Deposition (Cree / Charles & Colvard), HTCVD — High-Temperature CVD variants). Distinguishing natural from synthetic typically requires microscopic examination of internal features.
- General Note: There is no gem-quality natural moissanite. All moissanite presented as a gemstone is synthetic SiC. The relevant question is distinguishing moissanite from diamond. Synthetic: Key features of moissanite vs. diamond: (1) Strong facet doubling visible through table under 10× loupe — diamond shows none. (2) RI 2.648–2.691 — off refractometer scale. (3) SG ~3.22 vs diamond ~3.52. (4) Basic thermal tester may read 'diamond' — always follow up with electrical conductance tester or doubling check. (5) Strong LW fluorescence (often orange or yellow) — different from typical diamond blue.
Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Moissanite.
Common Simulants
- Diamond: Diamond is singly refractive (SR) — no facet doubling; thermal probe reads hot; RI 2.42 vs moissanite 2.65–2.69.
Commonly Confused With
Commonly confused with: Diamond.
Treatments
- Surface Coating (to create colored moissanite)
Related Comparisons
Measurement Guides
Identifying a moissanite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Moissanite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →