Chrysoberyl (Cat's-Eye) Gemstone & Information | Gemopedia by JTV | Gemopedia™
The term cat's eye is used to describe a phenomenal optical property in gemstones, but in this case, chrysoberyl. Known as chatoyancy, this effect appears as a bright, narrow slit--similar to the pupils in the eyes of your favorite feline. This phenomenon is caused by the presence of parallel fibrous or needle-like inclusions that interfere with the passage of light through the crystal, scattering and reflecting light back to the viewer as a thin line.
Yellow To Yellowish Green, Grayish Green, Brown To Brownish Yellow
Chrysoberyl-cats-eye classificationCommonNameChrysoberyl (Cat's-Eye)SpeciesChrysoberylVarietyCat's-Eye ChrysoberylColorsYellow To Yellowish Green, Grayish Green, Brown To Brownish YellowAlternateNamesCymophane, Cat's-EyeGemstoneGroupsKeySeparationsrefractive index, specific gravity, appearance and spectrum. Spectrum should reflect a strong diagnostic band at 444nm.ClassificationCommentsPhenomenal chrysoberyl may exhibit chatoyancy, in which case it is classified as "cat's-eye chrysoberyl." Cymophane will show a broad sheen instead of a distinct cat's-eye. Most often seen with yellowish green to orangy yellow background with strong silvery white cat's-eye.Cat's-eye chrysoberyl is the only chatoyant stone allowed to be called by only the name cat's-eye. Rare stones might show 4 rayed stars.
Chrysoberyl-cats-eye chemistry & crystallographyChemicalNameberyllium aluminum oxideChemicalFormulaBeAl2O4SynthesisCrystalSystemOrthorhombicChemistryClassificationOxideNatureNaturalCrystallinityCrystallineChemistryComments
Chrysoberyl-cats-eye optical propertiesTransparencySemitransparent - TranslucentDispersionStrength: weak fire Value: 0.015OpticalCommentsRefractiveIndex1.746-1.755
Tolerance:(+0.004/-0.006)Birefringence0.008-0.01OpticCharacterBiaxialOpticSignPositivePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert
Chrysoberyl-cats-eye characteristic physical propertiesHardness8.5CharacteristicCommentsStreakWhiteSpecificGravity3.71-3.75 Range:+/-0.02 Typical:3.73ToughnessVariesInclusionsCat's-eye chrysoberyl will have parallel rutile needles or hollow growth tubes parallel to the c-axis that have give the appearance of silk. Stone can contain fingerprints or liquid inclusions and have angular included crystals. Stone might show twinningLusterBright VitreousStabilityVery GoodFractureConchoidalCleavageGood, in one direction, Poor, in two directions