Star Corundum (Lattice-Diffused) Gemstone & Information | Gemopedia by JTV | Gemopedia™
Corundum with star induced by lattice diffusion has been treated with a heat treatment at high temperatures with beryllium that deeply penetrates the gem material to alter the color. This gem exhibits the optical phenomenon called asterism, a star-like pattern created on the surface of a gemstone when light encounters parallel fibrous, or needle-like, inclusions within its crystal structure. Light that strikes the inclusions within the gem reflects off of the inclusions, creating narrow bands of light.
Star-corundum-lattice-diffused classificationCommonNameStar Corundum (Lattice-Diffused)SpeciesCorundumVarietyLattice Diffused Star CorundumColorsBlueAlternateNamesCorundum With Star Induced By Lattice DiffusionGemstoneGroupsKeySeparationsmagnification and appearanceClassificationComments
Star-corundum-lattice-diffused chemistry & crystallographyChemicalNamealuminum oxideChemicalFormulaAl2O3SynthesisCrystalSystemTrigonalChemistryClassificationOxideNatureNaturalCrystallinityCrystallineChemistryComments
Star-corundum-lattice-diffused optical propertiesTransparencySemitransparent - OpaqueDispersionStrength: weak fire Value: 0.018OpticalCommentsRefractiveIndex1.762-1.77
Tolerance:(+0.009/-0.005)Birefringence0.008-0.01OpticCharacterUniaxialOpticSignNegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert to strong red
LWUV: weak to strong redCCFReactionPleochroismUnobservable
Star-corundum-lattice-diffused characteristic physical propertiesHardness9CharacteristicCommentsStreakWhiteSpecificGravity4.1-3.95 Typical:4ToughnessVariesInclusionsStars that are induced by lattice diffusion will have a unnaturally sharp or well defined star. The color of the stone is confined to the surface and concentrated around the girdle edge. The stone can have color concentrations in the pits and fractures. None of the rays of the star are perpendicular to the stone's hexagonal growth structure.LusterSubAdamantineStabilityVery GoodFractureConchoidalCleavageNone