Alexandrite Gemstone & Information | Gemopedia by JTV | Gemopedia™

Alexandrite

Alexandrite is the rare color-change variety of the mineral chrysoberyl. Its rarity is a result of its unlikely chemical makeup. Alexandrite can only form when aluminum and beryllium combine with trace elements like iron, titanium and, most importantly, chromium. On rare occasion, vanadium may also be present. The unlikelihood of the rare element chromium being in the right place to combine with aluminum and beryllium under exactly the right conditions to create alexandrite is what makes it so rare and valuable.

Colors

In Incandescent Light: Orangy, Brownish Red To Purplish Red; In Fluorescent, Daylight: Yellowish, Brownish, Grayish, Bluish Green

  • Alexandrite classification

    CommonName
    Alexandrite
    Species
    Chrysoberyl
    Variety
    Alexandrite
    Colors
    In Incandescent Light: Orangy, Brownish Red To Purplish Red; In Fluorescent, Daylight: Yellowish, Brownish, Grayish, Bluish Green
    AlternateNames
    GemstoneGroups
    KeySeparations
    Color change, refractive index, birefringence, pleochroism and spectrum
    ClassificationComments
    Alexandrite's spectrum varies by direction, showing a different spectrum in the green direction than in the purple-red pleochroic direction. Green, blue-green to pale green, yellowish, brownish, grayish in daylight or fluorescent light and violet, purplish to red, orangy or brownish in incandescent light.
  • Alexandrite chemistry & crystallography

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

    Transparency
    Transparent
    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 characteristic physical properties

    Hardness
    8.5
    CharacteristicComments
    Streak
    White
    SpecificGravity
    3.71-3.75 Range:+/- 0.02 Typical:3.73
    Toughness
    Varies
    Inclusions
    Alexandrite is a type II clarity stone. The stone may contain fluorite, apatite, mica platlets, rutile and multi-phase inclusions along with negative crystals, fingerprints, liquid inclusions, needles and hollow tubes. Alexandrite's might show twinning.
    Luster
    Bright Vitreous
    Stability
    Very Good
    Fracture
    Conchoidal
    Cleavage
    Good, in one direction