Boulder Opal Gemstone & Information | Gemopedia by JTV | Gemopedia™

Boulder Opal

Known for its lively, flaming color displays, boulder opal is in high demand by collectors and jewelry designers. As opposed to cut opal gems, boulder opal features small opal veins running through its matrix. The precious opal's rainbow of colors make a dramatic contrast to the rich earthy reds and browns of the host rock, creating a one-of-a-kind display.

Colors

Brown With Seams Of Play-Of-Color

  • Boulder-opal classification

    CommonName
    Boulder Opal
    Species
    Opal
    Variety
    Boulder Opal
    Colors
    Brown With Seams Of Play-Of-Color
    AlternateNames
    Precious Opal, Natural Opal Type 2, Yowah Opal
    GemstoneGroups
    KeySeparations
    Appearance, RI and fluorescence
    ClassificationComments
    Yowah opal is a boulder matrix opal that is cut to display the small seams mixed through out the ironstone.
  • Boulder-opal chemistry & crystallography

    ChemicalName
    hydrated silicon dioxide
    ChemicalFormula
    SiO2-nH2O
    Synthesis
    CrystalSystem
    NA
    ChemistryClassification
    Silicate
    Nature
    Natural
    Crystallinity
    Amorphous
    ChemistryComments
  • Boulder-opal optical properties

    Transparency
    Transparent - Opaque
    Dispersion
    Strength: none
    OpticalComments
    RefractiveIndex
    1.45
    Tolerance:(+0.020/-0.080)
    Birefringence
    OpticCharacter
    NA
    OpticSign
    PolariscopeReaction
    Singly Refractive (SR) With ADR
    Fluorescence
    SWUV: Variable
    LWUV: Variable
    CCFReaction
    Pleochroism
    None
  • Boulder-opal characteristic physical properties

    Hardness
    5-6.5
    CharacteristicComments
    Streak
    SpecificGravity
    1.98-2.25
    Toughness
    Varies
    Inclusions
    Boulder opal will have seams of precious opal in brown ironstone, quartzite, rhyolite or basalt host rock.
    Luster
    Vitreous
    Stability
    Fracture
    Conchoidal, Uneven
    Cleavage
    None