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

Alexandrite (Cat's-Eye)

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

  • Alexandrite-cats-eye classification

    CommonName
    Alexandrite (Cat's-Eye)
    Species
    Chrysoberyl
    Variety
    Cat's-Eye Alexandrite
    Colors
    Daylight Yellowish, Brownish, Grayish, Blueish Green. Incandescent Light: Orangy, Brownish Red To Purple Red
    AlternateNames
    GemstoneGroups
    KeySeparations
    Cat's-eye and color change, RI, SG and spectrum.
    ClassificationComments
  • Alexandrite-cats-eye chemistry & crystallography

    ChemicalName
    beryllium aluminum oxide
    ChemicalFormula
    BeAl2O4
    Synthesis
    CrystalSystem
    Orthorhombic
    ChemistryClassification
    Oxide
    Nature
    Natural
    Crystallinity
    Crystalline to Aggregate
    ChemistryComments
  • Alexandrite-cats-eye optical properties

    Transparency
    Semitransparent - Semitranslucent
    Dispersion
    Strength: weak fire Value: 0.015
    OpticalComments
    RefractiveIndex
    1.746-1.755
    Tolerance:(+0.004/-0.006)
    Birefringence
    0.008-0.01
    OpticCharacter
    Biaxial
    OpticSign
    Positive
    PolariscopeReaction
    Doubly Refractive (DR)
    Fluorescence
    SWUV: Inert to moderate red
    LWUV: Inert to moderate red
    CCFReaction
    red
    Pleochroism
    Trichroic, strong green, orange and purplish red
  • Alexandrite-cats-eye characteristic physical properties

    Hardness
    8.5
    CharacteristicComments
    Streak
    White
    SpecificGravity
    3.71-3.75 Typical:3.73
    Toughness
    Excellent
    Inclusions
    Natural 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.
    Luster
    SubAdamantine
    Stability
    Very Good
    Fracture
    Conchoidal
    Cleavage
    Good, in one direction, Poor, in two directions