Oligoclase Gemstone & Information | Gemopedia by JTV | Gemopedia™

Oligoclase

Oligoclase is a member of the plagioclase feldspar group. Two oligoclase varieties, sunstone and moonstone, are prized for their phenomenal optical properties.

Colors

Yellow, Brown To Orange, Brownish Red, Colorless, White To Light Green, Gray

  • Oligoclase classification

    CommonName
    Oligoclase
    Species
    Oligoclase
    Variety
    Colors
    Yellow, Brown To Orange, Brownish Red, Colorless, White To Light Green, Gray
    AlternateNames
    GemstoneGroups
    Feldspar
    KeySeparations
    appearance, RI, birefringence and optic character.
    ClassificationComments
    If adventurescence is present then the stone is sunstone.
  • Oligoclase chemistry & crystallography

    ChemicalName
    calcium or sodium silicate
    ChemicalFormula
    NaAlSi3O8 or CaAl2Si2O8
    Synthesis
    CrystalSystem
    Triclinic
    ChemistryClassification
    Silicate
    Nature
    Natural
    Crystallinity
    Crystalline to Aggregate
    ChemistryComments
  • Oligoclase optical properties

    Transparency
    Translucent - Opaque
    Dispersion
    OpticalComments
    RefractiveIndex
    1.539-1.547
    Tolerance:(+0.004/-0.006)
    Birefringence
    0.007-0.01
    OpticCharacter
    Biaxial
    OpticSign
    Negative
    PolariscopeReaction
    Doubly Refractive (DR)
    Fluorescence
    SWUV: Inert
    LWUV: Inert
    CCFReaction
    Pleochroism
    Unobservable
  • Oligoclase characteristic physical properties

    Hardness
    6-6.5
    CharacteristicComments
    Streak
    SpecificGravity
    2.62-2.67 Typical:2.65
    Toughness
    Poor
    Inclusions
    Oligoclase feldspar has parallel closely spaced twinning planes. Transparent material might show eye-visible iridescent platelets.
    Luster
    Vitreous
    Stability
    Good
    Fracture
    Uneven, Splintery
    Cleavage
    Perfect, in two directions