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

Tourmaline (Cat's-Eye)

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.

Colors

Most Often Dark Bluish Green To Dark Greenish Blue But Can Be Any Color

  • Tourmaline-cats-eye classification

    CommonName
    Tourmaline (Cat's-Eye)
    Species
    Elbaite
    Variety
    Cat's-Eye Tourmaline
    Colors
    Most Often Dark Bluish Green To Dark Greenish Blue But Can Be Any Color
    AlternateNames
    GemstoneGroups
    Tourmaline
    KeySeparations
    appearance, refractive index and high birefringence; then optic figure, pleochroism and specific gravity
    ClassificationComments
    Not 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 & crystallography

    ChemicalName
    complex boro-silicate of Al, Mg and Fe
    ChemicalFormula
    Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
    Synthesis
    CrystalSystem
    Trigonal
    ChemistryClassification
    Silicate
    Nature
    Natural
    Crystallinity
    Crystalline
    ChemistryComments
  • Tourmaline-cats-eye optical properties

    Transparency
    Transparent - Translucent
    Dispersion
    Strength: moderate fire Value: 0.017
    OpticalComments
    RefractiveIndex
    1.624-1.644
    Tolerance:-1.22222222222222
    Birefringence
    0.018-0.02
    OpticCharacter
    Uniaxial
    OpticSign
    Negative
    PolariscopeReaction
    Doubly Refractive (DR)
    Fluorescence
    SWUV: Variable Pink: inert to very weak red to violet
    LWUV: Variable Pink: inert to very weak red to violet
    CCFReaction
    Pleochroism
    Dichroic, medium to strong variations of bodycolor
  • Tourmaline-cats-eye characteristic physical properties

    Hardness
    7-7.5
    CharacteristicComments
    Streak
    White
    SpecificGravity
    3-3.26 Typical:3.06
    Toughness
    Good
    Inclusions
    Cat'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.
    Luster
    Vitreous
    Stability
    Very Good
    Fracture
    Conchoidal, Subconchoidal, Irregular, Uneven
    Cleavage
    Poor, in two directions