Properties of Diamond SimulantsProperties of Diamond Simulants

Diamond Specialist Certification Course

Properties of Diamond Simulants

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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.

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Learn the fundamentals of diamonds — from optical and physical properties to grading and ethical and legal issues. Learn to distinguish natural diamonds from synthetics and diamond simulants. Keep the kit, which includes one natural, jewelry-grade diamond. If you successfully pass the quiz and gem identification test, then you will be an IGS-certified Diamond Specialist.
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

PropertiesNatural Diamond Type IaNatural Diamond Type IbNatural Diamond Type IIaNatural Diamond Type IIbMoissaniteCubic Zirconia
RI2.4172.4172.4172.4172.648 - 2.6912.15 - 2.18
Dispersion. - .104.058 - .066
Optic CharacterIsotropicIsotropicIsotropicIsotropicUniaxial +Isotropic
Read ThroughNoneNoneNoneNoneNoneSlight
SG3.5153.5153.5153.5153.17 - 3.225.56 - 6.00
Hardness101010109 ¼8 - 8 ½
CleavagePerfect, four directionsPerfect, four directionsPerfect, four directionsPerfect, four directionsNoneNone
Absorption SpectraDark line at 415 and 478 nm, often moreIncreasing absorption towards blue endVariable, usually 504VariableNo sharp bands, strong absorption below 425Not diagnostic
UVColorless stones, inert to strong, usually blue (LW) Weaker (SW)Variable, can be inert, usually blue or yellowVariable, can be inert, often redInert but phosphoresce after exposure to SW UVBrownish yellow, (LW)Greenish/yellow or orangish/yellow (LW) Yellow (SW) Colored CZ varies
Girdle SurfaceWaxy, polished or granularWaxy, polished or granularWaxy, polished or granularWaxy, polished or granularFrosted, polished or striatedFrosted or polished
Facet JunctionsSharpSharpSharpSharpSharp or slightly roundedSharp or slightly rounded
Electrical TestNoneNoneVery WeakStrongFrequent, variable intensityNone
Thermal Test"Diamond""Diamond""Diamond""Diamond""Diamond""Simulant"
InclusionsBearding, crystals, planar grainingBearding, crystals, planar grainingBearding, crystals, planar grainingBearding, crystals, planar grainingBearding, crystals, planar grainingGas bubbles, negative crystals, unmelted powder
PropertiesGGGYAGSynthetic Spinel*White SapphireWhite TopazGlass
RI1.970 - 2.031.823 - 1.8431.720 - 1.7401.757 - 1.7791.609 - 1.6371.40 - 1.70
BirefringenceNoneNoneNone.008 - .010.008 - .010None
Dispersion.038 - . - .098
Optic CharacterIsotropicIsotropicIsotropicUniaxial -Biaxial +Amorphous
PleochroismNoneNoneNoneNone if totally colorlessNone if totally colorlessNone
Read ThroughModerateStrongStrongStrongStrongStrong
LusterVitreous to subadamantineVitreous to subadamantineVitreous to subadamantineVitreous to subadamantineVitreousVitreous
SG7.01 - 7.154.50 - 4.603.52 - 3.673.90 - 4.103.49 - 3.572.30 - 4.50
Hardness6.5 - 78.25 - 8.57.5 - 8985 - 6
CleavageNoneNoneNoneNonePerfect, 1 directionNone
Absorption SpectraNot diagnosticNot diagnosticNot diagnosticNot diagnosticNot diagnosticNot diagnostic
UVModerate 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 diagnosticNot diagnostic
Girdle SurfaceFrosted or polishedFrosted or polishedFrosted or polishedFrosted or polishedFrosted or polishedFrosted or polished
Facet JunctionsSlightly roundedSharp or slightly roundedSharp or slightly roundedSharp or slightly roundedSharp or slightly roundedRounded
Electrical TestNoneNoneNoneNoneNoneNone
Thermal Test"Simulant""Simulant""Simulant""Simulant""Simulant""Simulant"
InclusionsGas bubblesGas bubbles, curved striaeGas bubblesNatural: Silk, crystals, fingerprint, hexagonal banding. Synthetic: bubbles, curved striae, flux2 & 3 phaseBubbles, swirl lines, concave facets

Compliments of the International Gem Society.


* 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.

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