Andalusite Gemstone & Information | Gemopedia by JTV | Gemopedia™

Andalusite

Andalusite, an aluminum silicate, derives its name from the southern Spanish province of Andalusia, long believed to be the sight of its original discovery. Many now feel the original find may have actually occurred in El Cardoso, a different province in Spain, but the name endured. While andalusite's color play has been compared to alexandrite, this is technically incorrect, as it is pleochroic rather than color changing. Prized for its strong pleochroism, it displays different colors in different directions and features all its colors at once, whereas true color-change gems like alexandrite only change color when exposed to different light sources.

Colors

Yellowish Green To Brownish Green, Orangy Brown

  • Andalusite classification

    CommonName
    Andalusite
    Species
    Andalusite
    Variety
    Colors
    Yellowish Green To Brownish Green, Orangy Brown
    AlternateNames
    Viridine, Chiastolite
    GemstoneGroups
    KeySeparations
    Pleochroism is usually evident from general observation. Identity may be confirmed by refractive index, birefringence, and optic character.
    ClassificationComments
    Andalusite is a polymorph of Al2SiO5 along with kyanite and sillimanite. Misnomers: poor man's alexandrite. Viridine is the dark green variety containing iron and manganese. Chiastolite is translucent to opaque and displays a cross.
  • Andalusite chemistry & crystallography

    ChemicalName
    aluminum silicate
    ChemicalFormula
    Al2SiO5
    Synthesis
    CrystalSystem
    Orthorhombic
    ChemistryClassification
    Silicate
    Nature
    Natural
    Crystallinity
    Crystalline
    ChemistryComments
  • Andalusite optical properties

    Transparency
    Transparent - Opaque
    Dispersion
    Strength: weak fire Value: 0.016
    OpticalComments
    RefractiveIndex
    1.634-1.643
    Tolerance:(+0.005/-0.005)
    Birefringence
    0.007-0.013
    OpticCharacter
    Biaxial
    OpticSign
    Negative
    PolariscopeReaction
    Doubly Refractive (DR)
    Fluorescence
    SWUV: Inert to moderate green to yellowish green
    LWUV: Inert
    CCFReaction
    Pleochroism
    Trichroic, strong yellowish green, green and brownish red
  • Andalusite characteristic physical properties

    Hardness
    7.5
    CharacteristicComments
    Streak
    White
    SpecificGravity
    Typical:3.17
    Toughness
    Varies
    Inclusions
    Andalusite is a type II clarity stone. The needles or crystals seen in the stone are most likely rutile and apatite.
    Luster
    Vitreous
    Stability
    Good
    Fracture
    Uneven
    Cleavage
    Good, in one direction, Poor, in one direction