Blue John Gemstone & Information | Gemopedia by JTV | Gemopedia™
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.
Bluish Violet To Purple Bands In A Reddish To Colorless Background
Blue-john classificationCommonNameBlue JohnSpeciesFluoriteVarietyBlue JohnColorsBluish Violet To Purple Bands In A Reddish To Colorless BackgroundAlternateNamesGemstoneGroupsKeySeparationsAppearance, refractive index, specific gravity and possibly cleavageClassificationCommentsBlue John was first found in the Blue John Cavern in Castleton, Derbyshire, England.
Blue-john chemistry & crystallographyChemicalNamecalcium fluorideChemicalFormulaCaF2SynthesisCrystalSystemCubicChemistryClassificationHalideNatureNaturalCrystallinityCrystallineChemistryComments
Blue-john optical propertiesTransparencyTransparent To TranslucentDispersionStrength: weak fire Value: 0.007OpticalCommentsRefractiveIndex1.434-1.434
Tolerance: (+0.001/-0.001)BirefringenceOpticCharacterNAOpticSignNAPolariscopeReactionSingly Refractive (SR)FluorescenceSWUV: Variable
Blue-john characteristic physical propertiesHardness4CharacteristicCommentsStreakWhiteSpecificGravity3-3.25 Typical: 3.18ToughnessPoorInclusionsBlue 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.LusterVitreousStabilityFairFractureConchoidal, Step-LikeCleavagePerfect, in four directions