Tourmaline (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 tourmaline. 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. Cat's eye tourmaline can occur in many colors but particularly in green and pink varieties.
Most Often Dark Bluish Green To Dark Greenish Blue But Can Be Any Color
Tourmaline-cats-eye classificationCommonNameTourmaline (Cat's-Eye)SpeciesElbaiteVarietyCat's-Eye TourmalineColorsMost Often Dark Bluish Green To Dark Greenish Blue But Can Be Any ColorAlternateNamesGemstoneGroupsTourmalineKeySeparationsappearance, refractive index and high birefringence; then optic figure, pleochroism and specific gravityClassificationCommentsNot all cat's-eye tourmaline is elbaite Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH). Dark material might have birefringence as high as 0.040. Pyroelectric: development of opposite charges at the ends of a tourmaline crystal due to change in temperature. Piezoelectric: development of opposite charges at the ends of a tourmaline crystal when placed under stress.
Tourmaline-cats-eye chemistry & crystallographyChemicalNamecomplex boro-silicate of Al, Mg and FeChemicalFormulaNa(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)SynthesisCrystalSystemTrigonalChemistryClassificationSilicateNatureNaturalCrystallinityCrystallineChemistryComments
Tourmaline-cats-eye optical propertiesTransparencyTransparent - TranslucentDispersionStrength: moderate fire Value: 0.017OpticalCommentsRefractiveIndex1.624-1.644
Tolerance:-1.22222222222222Birefringence0.018-0.02OpticCharacterUniaxialOpticSignNegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Variable Pink: inert to very weak red to violet
LWUV: Variable Pink: inert to very weak red to violetCCFReactionPleochroismDichroic, medium to strong variations of bodycolor
Tourmaline-cats-eye characteristic physical propertiesHardness7-7.5CharacteristicCommentsStreakWhiteSpecificGravity3-3.26 Typical:3.06ToughnessGoodInclusionsCat's-eye tourmaline has Type III clarity. Stones has numerous parallel hollow tubes. The eye is less focused and harder to see than other cat's-eye stones. Stones might have liquid and gas inclusions that are long and thin, reflective gas-filled fractures and color zoning.LusterVitreousStabilityVery GoodFractureConchoidal, Subconchoidal, Irregular, UnevenCleavagePoor, in two directions