Two pear-cut moissanites in an infinity setting. © CustomMade. Used with permission.
This information, in conjunction with our article on distinguishing diamonds, can help you separate diamonds from their imitators.
Identifying Synthetic Diamonds
Until relatively recently, gem-grade synthetic diamonds rarely appeared in jewelry. This is changing. Consult our article on identifying synthetic diamonds for advice on distinguishing natural or mined diamonds from their lab-created counterparts.
Properties of Natural Diamonds vs. Diamond Simulants
Properties | Natural Diamond Type Ia | Natural Diamond Type Ib | Natural Diamond Type IIa | Natural Diamond Type IIb | Moissanite | Cubic Zirconia |
---|---|---|---|---|---|---|
RI | 2.417 | 2.417 | 2.417 | 2.417 | 2.648 – 2.691 | 2.15 – 2.18 |
Birefringence | None | None | None | None | .043 | None |
Dispersion | .044 | .044 | .044 | .044 | .009 – .104 | .058 – .066 |
Optic Character | Isotropic | Isotropic | Isotropic | Isotropic | Uniaxial + | Isotropic |
Pleochroism | None | None | None | None | None | None |
Read Through | None | None | None | None | None | Slight |
Luster | Adamantine | Adamantine | Adamantine | Adamantine | Adamantine | Subadamantine |
SG | 3.515 | 3.515 | 3.515 | 3.515 | 3.17 – 3.22 | 5.56 – 6.00 |
Hardness | 10 | 10 | 10 | 10 | 9 ¼ | 8 – 8 ½ |
Cleavage | Perfect, four directions | Perfect, four directions | Perfect, four directions | Perfect, four directions | None | None |
Absorption Spectra | Dark line at 415 and 478 nm, often more | Increasing absorption towards blue end | Variable, usually 504 | Variable | No sharp bands, strong absorption below 425 | Not diagnostic |
UV | Colorless stones, inert to strong, usually blue (LW) Weaker (SW) | Variable, can be inert, usually blue or yellow | Variable, can be inert, often red | Inert but phosphoresce after exposure to SW UV | Brownish yellow, (LW) | Greenish/yellow or orangish/yellow (LW) Yellow (SW) Colored CZ varies |
Girdle Surface | Waxy, polished or granular | Waxy, polished or granular | Waxy, polished or granular | Waxy, polished or granular | Frosted, polished or striated | Frosted or polished |
Facet Junctions | Sharp | Sharp | Sharp | Sharp | Sharp or slightly rounded | Sharp or slightly rounded |
Electrical Test | None | None | Very Weak | Strong | Frequent, variable intensity | None |
Thermal Test | “Diamond” | “Diamond” | “Diamond” | “Diamond” | “Diamond” | “Simulant” |
Inclusions | Bearding, crystals, planar graining | Bearding, crystals, planar graining | Bearding, crystals, planar graining | Bearding, crystals, planar graining | Bearding, crystals, planar graining | Gas bubbles, negative crystals, unmelted powder |
Properties | GGG | YAG | Synthetic Spinel* | White Sapphire | White Topaz | Glass |
---|---|---|---|---|---|---|
RI | 1.970 – 2.03 | 1.823 – 1.843 | 1.720 – 1.740 | 1.757 – 1.779 | 1.609 – 1.637 | 1.40 – 1.70 |
Birefringence | None | None | None | .008 – .010 | .008 – .010 | None |
Dispersion | .038 – .045 | .028 | .020 | .018 | .014 | .009 – .098 |
Optic Character | Isotropic | Isotropic | Isotropic | Uniaxial – | Biaxial + | Amorphous |
Pleochroism | None | None | None | None if totally colorless | None if totally colorless | None |
Read Through | Moderate | Strong | Strong | Strong | Strong | Strong |
Luster | Vitreous to subadamantine | Vitreous to subadamantine | Vitreous to subadamantine | Vitreous to subadamantine | Vitreous | Vitreous |
SG | 7.01 – 7.15 | 4.50 – 4.60 | 3.52 – 3.67 | 3.90 – 4.10 | 3.49 – 3.57 | 2.30 – 4.50 |
Hardness | 6.5 – 7 | 8.25 – 8.5 | 7.5 – 8 | 9 | 8 | 5 – 6 |
Cleavage | None | None | None | None | Perfect, 1 direction | None |
Absorption Spectra | Not diagnostic | Not diagnostic | Not diagnostic | Not diagnostic | Not diagnostic | Not diagnostic |
UV | Moderate to strong, pinkish orange (SW) | Inert to moderate orange, (LW) Inert to weak orange, (SW) | Occasionally, weak green (LW) Moderate to strong chalky or greenish blue, (SW) | Natural: Inert to moderate red to orange (LW & SW)Synthetic: inert to weak, blueish white (SW) | Not diagnostic | Not diagnostic |
Girdle Surface | Frosted or polished | Frosted or polished | Frosted or polished | Frosted or polished | Frosted or polished | Frosted or polished |
Facet Junctions | Slightly rounded | Sharp or slightly rounded | Sharp or slightly rounded | Sharp or slightly rounded | Sharp or slightly rounded | Rounded |
Electrical Test | None | None | None | None | None | None |
Thermal Test | “Simulant” | “Simulant” | “Simulant” | “Simulant” | “Simulant” | “Simulant” |
Inclusions | Gas bubbles | Gas bubbles, curved striae | Gas bubbles | Natural: Silk, crystals, fingerprint, hexagonal banding. Synthetic: bubbles, curved striae, flux | 2 & 3 phase | Bubbles, swirl lines, concave facets |
Compliments of the International Gem Society.
Notes
* Colorless natural spinels are extremely rare. Should you encounter a colorless spinel as a diamond simulant, it’s very likely synthetic.
For information on diamond color treatments, see our article on HPHT diamonds.