Gahnite Gemstone & Information | Gemopedia by JTV | Gemopedia™

Gahnite

Ranging from dark green to black in color, gahnite is a rare member of the spinel group. It was first discovered in Sweden 1807 and named in honor of Swedish chemist J.G. Gahn, who is credited with the discovery of manganese. While highly prized by mineral collectors for its octahedral crystal formation, gahnite is on occasion cut into faceted gems.

Colors

Red-Violet, Blue, Green, Black

  • Gahnite classification

    CommonName
    Gahnite
    Species
    Gahnite
    Variety
    Colors
    Red-Violet, Blue, Green, Black
    AlternateNames
    Zinc Spinel
    GemstoneGroups
    Spinel
    KeySeparations
    OTL RI, appearance and no dispersion.
    ClassificationComments
    Gahnite belongs to the spinel group but has a zinc in its chemistry.
  • Gahnite chemistry & crystallography

    ChemicalName
    zinc aluminum oxide
    ChemicalFormula
    ZnAl2O4
    Synthesis
    CrystalSystem
    Cubic
    ChemistryClassification
    Oxide
    Nature
    Natural
    Crystallinity
    Crystalline
    ChemistryComments
  • Gahnite optical properties

    Transparency
    Transparent - Translucent
    Dispersion
    OpticalComments
    RefractiveIndex
    1.8
    Tolerance:(+0.005/-0.010)
    Birefringence
    OpticCharacter
    NA
    OpticSign
    PolariscopeReaction
    Singly Refractive (SR)
    Fluorescence
    SWUV:
    LWUV:
    CCFReaction
    Pleochroism
    None
  • Gahnite characteristic physical properties

    Hardness
    7.5-8
    CharacteristicComments
    Streak
    Gray-White
    SpecificGravity
    4.4-4.63 Typical:4.55
    Toughness
    Poor
    Inclusions
    Luster
    Vitreous
    Stability
    Fracture
    Uneven
    Cleavage
    None