Diamond simulants often appear in jewelry, as side stones and accents as well as centerpieces. Identifying these lookalike materials, whether glass, cubic zirconia, or natural gems that resemble diamonds, is an important skill for gemologists. The chart below compares the physical and optical properties of natural diamonds with those of frequently encountered diamond simulants.
By International Gem Society 3 minute read
moissanites in infinity setting - diamond simulants

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.

diamond simulants - moissanite ring

Moissanite engagement/wedding ring. Photo by 3BL Media. Licensed under CC By 2.0.