Diamond and Simulant Comparison Chart

Properties Natural Diamond Type Ia Natural Diamond Type Ib Natural Diamond Type IIa Natural Diamond Type IIb Moissanite Cubic Zirconium
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
ReadThrough 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 5040 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 Sapphires 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
ReadThrough 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, bluish 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

* Natural spinel is never colorless Also, see our article on HPHT treated diamonds.

Diamond and Simulant Comparison Chart

Compliments of The International Gem Society

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