Star Ruby Gemstone & Information | Gemopedia by JTV | Gemopedia™
Star ruby 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 a narrow band of light. When two or more intersecting bands appear, a star pattern is formed. Depending on the crystal, the star may have four, six, or even twelve rays. When only one band forms, it is classified as a "cat's eye".
Red, Orangy Red To Purplish Red
Star-ruby classificationCommonNameStar RubySpeciesCorundumVarietyStar RubyColorsRed, Orangy Red To Purplish RedAlternateNamesGemstoneGroupsKeySeparationsAppearance, RI and magnificationClassificationCommentsStones are usually cut as cabochons.
Star-ruby chemistry & crystallographyChemicalNamealuminum oxideChemicalFormulaAl2O3SynthesisCrystalSystemTrigonalChemistryClassificationOxideNatureNaturalCrystallinityCrystalline to AggregateChemistryComments
Star-ruby optical propertiesTransparencySemitransparent - OpaqueDispersionStrength: moderate fire Value: 0.018OpticalCommentsRefractiveIndex1.762-1.77
Tolerance:(+0.009/-0.005)Birefringence0.008-0.01OpticCharacterUniaxialOpticSignNegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Weak to strong red
LWUV: Weak to strong redCCFReactionPleochroismUnobservable
Star-ruby characteristic physical propertiesHardness9CharacteristicCommentsStreakWhiteSpecificGravity4.1-3.95 Typical:4ToughnessVariesInclusionsStar rubies will have silk or sets of parallel rutile needles that produce a 6-rayed star, hexagonal growth lines, color zoning, liquid, negative and mineral inclusions. Some stone might show twinning.LusterSubAdamantineStabilityVery GoodFractureConchoidalCleavageNone