Iolite Gemstone & Information | Gemopedia by JTV | Gemopedia™

Iolite

Iolite is the gem-quality blue or blue-violet variety of cordierite. While iolite enjoyed popularity in jewelry in 18th-century Europe, this naturally beautiful gemstone is relatively new to today's jewelry market, and is regaining popularity with the public. Because of its varying levels of hardness and strong pleochroism, iolite is one of the most difficult stones for lapidaries to fashion. It must be cut in certain directions to take advantage of the best color, which can be tough when the shape of the rough doesn't lend itself to cutting in that same direction.

Colors

Violet Through Slighty Violetish Blue, Rarely Colorless

  • Iolite classification

    CommonName
    Iolite
    Species
    Cordierite
    Variety
    Iolite
    Colors
    Violet Through Slighty Violetish Blue, Rarely Colorless
    AlternateNames
    Cordierite, Dichroite, Bloodshot Iolite
    GemstoneGroups
    KeySeparations
    visible pleochroism, refractive index, birefringence and optic character. Eye visible pleochroism.
    ClassificationComments
    Misnomer: water sapphire.
  • Iolite chemistry & crystallography

    ChemicalName
    magnesium aluminum silicate
    ChemicalFormula
    Mg2Al4Si5O18
    Synthesis
    CrystalSystem
    Orthorhombic
    ChemistryClassification
    Silicate
    Nature
    Natural
    Crystallinity
    Crystalline
    ChemistryComments
  • Iolite optical properties

    Transparency
    Transparent - Translucent
    Dispersion
    Strength: moderate fire Value: 0.017
    OpticalComments
    RefractiveIndex
    1.542-1.551
    Tolerance:(+0.045/-0.011)
    Birefringence
    0.008-0.012
    OpticCharacter
    Biaxial
    OpticSign
    Negative
    PolariscopeReaction
    Doubly Refractive (DR)
    Fluorescence
    SWUV: Inert
    LWUV: Inert
    CCFReaction
    Pleochroism
    Trichroic, violet, colorless to yellow, and light grayish blue
  • Iolite characteristic physical properties

    Hardness
    7-7.5
    CharacteristicComments
    Streak
    White
    SpecificGravity
    2.56-2.66 Range:+/-0.05 Typical:2.61
    Toughness
    Fair
    Inclusions
    Iolite is a type II clarity stone. Sometimes apatite, hematite, iron oxide, magnetite, mica and rutile, inclusions are seen. Bloodshot iolite is the adventuresent variety with red plate like hematite, iron oxide inclusions along with goethite.
    Luster
    Vitreous
    Stability
    Fair
    Fracture
    Conchoidal, Uneven
    Cleavage
    Good, in one direction, Poor, in two directions