Dravite (Tourmaline) Gemstone & Information | Gemopedia by JTV | Gemopedia™
Dravite is the dark yellow to brown variety of tourmaline. It is named after a deposit in modern day Slovenia near the Drave river.
Dark Yellow To Brownish Black
Dravite-tourmaline classificationCommonNameDravite (Tourmaline)SpeciesDraviteVarietyColorsDark Yellow To Brownish BlackAlternateNamesGemstoneGroupsTourmalineKeySeparationsappearance, refractive index and high birefringence; then optic figure, pleochroism and specific gravityClassificationCommentsNamed for the river Drau in the Republic of Slovenia.Dark stones might have a birefringence as high as 0.040.Pyroelectric: development of opposite charges at the ends of a tourmaline crystal due to change in temperature. Piezoelectric: development of opposite charges at the ends of a tourmaline crystal when placed under stress.
Dravite-tourmaline chemistry & crystallographyChemicalNameSodium magnesium boro-aluminum silicate hydroxideChemicalFormulaNa(Mg3)Al6(Si6O18)(BO3)3(OH)3(OH)SynthesisCrystalSystemTrigonalChemistryClassificationSilicateNatureNaturalCrystallinityCrystallineChemistryComments
Dravite-tourmaline optical propertiesTransparencyTransparent - TranslucentDispersionStrength: moderate fire Value: 0.017OpticalCommentsRefractiveIndex1.614-1.666Birefringence0.014-0.032OpticCharacterUniaxialOpticSignNegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert to weak
LWUV: Inert to weakCCFReactionPleochroismDichroic, strong pale yellow to colorless and yellow, green, or brown
Dravite-tourmaline characteristic physical propertiesHardness7CharacteristicCommentsStreakWhiteSpecificGravity3-3.26 Typical:3.06ToughnessGoodInclusionsDravite is a Type II clarity stone. Stones might have liquid and gas inclusions that are long and thin, reflective gas-filled fractures and color zoning.LusterVitreousStabilityVery GoodFractureConchoidal, UnevenCleavagePoor, in two directions