Blue John Gemstone & Information | Gemopedia by JTV | Gemopedia™

Blue John

Blue John is the banded purple and white or yellow variety of fluorite. The major source of this color-zoned fluorite is Castleton in Derbyshire, England, where it is found in at least 14 differently patterned veins.

Colors

Bluish Violet To Purple Bands In A Reddish To Colorless Background

  • Blue-john classification

    CommonName
    Blue John
    Species
    Fluorite
    Variety
    Blue John
    Colors
    Bluish Violet To Purple Bands In A Reddish To Colorless Background
    AlternateNames
    GemstoneGroups
    KeySeparations
    Appearance, refractive index, specific gravity and possibly cleavage
    ClassificationComments
    Blue John was first found in the Blue John Cavern in Castleton, Derbyshire, England.
  • Blue-john chemistry & crystallography

    ChemicalName
    calcium fluoride
    ChemicalFormula
    CaF2
    Synthesis
    CrystalSystem
    Cubic
    ChemistryClassification
    Halide
    Nature
    Natural
    Crystallinity
    Crystalline
    ChemistryComments
  • Blue-john optical properties

    Transparency
    Transparent To Translucent
    Dispersion
    Strength: weak fire Value: 0.007
    OpticalComments
    RefractiveIndex
    1.434-1.434
    Tolerance: (+0.001/-0.001)
    Birefringence
    OpticCharacter
    NA
    OpticSign
    NA
    PolariscopeReaction
    Singly Refractive (SR)
    Fluorescence
    SWUV: Variable
    LWUV: Variable
    CCFReaction
    Pleochroism
    None
  • Blue-john characteristic physical properties

    Hardness
    4
    CharacteristicComments
    Streak
    White
    SpecificGravity
    3-3.25 Typical: 3.18
    Toughness
    Poor
    Inclusions
    Blue John will sometimes have triangular negative crystals, mineral inclusions, color zoning, healing cracks 2-phase and 3-phase inclusions and liquid inclusions. Bluish violet to purple bands in a reddish to colorless background. Might have pits or scratches. Look to see if the stone has been impregnated with resin.
    Luster
    Vitreous
    Stability
    Fair
    Fracture
    Conchoidal, Step-Like
    Cleavage
    Perfect, in four directions