Star Sapphire Gemstone & Information | Gemopedia by JTV | Gemopedia™
Star sapphire 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 typically has six rays, but on occasion, twelve rays.
Blue, Black, Brown, Green, Purple, Plum, Rarely Orange, Yellow; If Any Other Color Than Blue Designate By Color
Star-sapphire classificationCommonNameStar SapphireSpeciesCorundumVarietyStar SapphireColorsBlue, Black, Brown, Green, Purple, Plum, Rarely Orange, Yellow; If Any Other Color Than Blue Designate By ColorAlternateNamesGemstoneGroupsKeySeparationsappearance, RI and magnificationClassificationCommentsStone usually cut as cabochons. Black star sapphires cover black dark brown, green and dark blue.
Star-sapphire chemistry & crystallographyChemicalNamealuminum oxideChemicalFormulaAl2O3SynthesisCrystalSystemHexagonalChemistryClassificationOxideNatureNaturalCrystallinityCrystallineChemistryComments
Star-sapphire 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: Inert to strong redCCFReactionPleochroismUnobservable
Star-sapphire characteristic physical propertiesHardness9CharacteristicCommentsStreakWhiteSpecificGravity4.1-3.95 Typical:4ToughnessExcellentInclusionsStar sapphires will have silk or sets of parallel rutile needles that produce a 6-ray star, hexagonal growth lines, color zoning and mineral inclusions. Weak and less well formed stars along with weaker body color is typical of natural stones. In natural stones at least one ray of the start will be perpendicular to the hexagonal growth zones. Stone with 12-rayed stars are rare but typically occur in dark blue or black stones.LusterSubAdamantineStabilityVery GoodFractureConchoidalCleavageNone