Diamond and Simulant Comparison Chart

PropertiesNatural Diamond Type IaNatural Diamond Type IbNatural Diamond Type IIaNatural Diamond Type IIbMoissaniteCubic Zirconium
RI2.4172.4172.4172.4172.648 – 2.6912.15 – 2.18
BirefringenceNoneNoneNoneNone.043None
Dispersion.044.044.044.044.009 – .104.058 – .066
Optic CharacterIsotropicIsotropicIsotropicIsotropicUniaxial +Isotropic
PleochroismNoneNoneNoneNoneNoneNone
ReadThroughNoneNoneNoneNoneNoneSlight
LusterAdamantineAdamantineAdamantineAdamantineAdamantineSubadamantine
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 5040VariableNo 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 SapphiresWhite 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 – .045.028.020.018.014.009 – .098
Optic CharacterIsotropicIsotropicIsotropicUniaxial -Biaxial +Amorphous
PleochroismNoneNoneNoneNone if totally colorlessNone if totally colorlessNone
ReadThroughModerateStrongStrongStrongStrongStrong
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, bluish 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

* 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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