Alexandrite (Cat's-Eye) Gemstone & Information | Gemopedia by JTV | Gemopedia™

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case chrysoberyl. The effect, when present, appears as a bright, narrow slit similar to the pupils in the eyes of your favorite feline. This phenomenon is caused by parallel fibrous or needle-like inclusions that interfere with the passage of light throughout the crystal, scattering and reflecting light back to the viewer as a thin line. Chatoyant chrysoberyl is particularly incredible because it exhibits two rare phenomena: both the cat's eye effect and color change.
Colors
Daylight Yellowish, Brownish, Grayish, Blueish Green. Incandescent Light: Orangy, Brownish Red To Purple Red
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Alexandrite-cats-eye classification
CommonNameAlexandrite (Cat's-Eye)SpeciesChrysoberylVarietyCat's-Eye AlexandriteColorsDaylight Yellowish, Brownish, Grayish, Blueish Green. Incandescent Light: Orangy, Brownish Red To Purple RedAlternateNamesGemstoneGroupsKeySeparationsCat's-eye and color change, RI, SG and spectrum.ClassificationComments -
Alexandrite-cats-eye chemistry & crystallography
ChemicalNameberyllium aluminum oxideChemicalFormulaBeAl2O4SynthesisCrystalSystemOrthorhombicChemistryClassificationOxideNatureNaturalCrystallinityCrystalline to AggregateChemistryComments -
Alexandrite-cats-eye optical properties
TransparencySemitransparent - SemitranslucentDispersionStrength: weak fire Value: 0.015OpticalCommentsRefractiveIndex1.746-1.755
Tolerance:(+0.004/-0.006)Birefringence0.008-0.01OpticCharacterBiaxialOpticSignPositivePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert to moderate red
LWUV: Inert to moderate redCCFReactionredPleochroismTrichroic, strong green, orange and purplish red -
Alexandrite-cats-eye characteristic physical properties
Hardness8.5CharacteristicCommentsStreakWhiteSpecificGravity3.71-3.75 Typical:3.73ToughnessExcellentInclusionsNatural cat's-eye alexandrite typically has fine needles or hollow tubes. The stones can have fluorite, apatite, mica platlets, rutile and multi-phase inclusions along with negative crystals, liquid and fingerprint inclusions. Some stones might show twinning.LusterSubAdamantineStabilityVery GoodFractureConchoidalCleavageGood, in one direction, Poor, in two directions