Iolite Gemstone & Information | Gemopedia by JTV | Gemopedia™
Iolite is the gem-quality blue or blue-violet variety of cordierite. While iolite enjoyed popularity in jewelry in 18th-century Europe, this naturally beautiful gemstone is relatively new to today's jewelry market, and is regaining popularity with the public. Because of its varying levels of hardness and strong pleochroism, iolite is one of the most difficult stones for lapidaries to fashion. It must be cut in certain directions to take advantage of the best color, which can be tough when the shape of the rough doesn't lend itself to cutting in that same direction.
Violet Through Slighty Violetish Blue, Rarely Colorless
Iolite classificationCommonNameIoliteSpeciesCordieriteVarietyIoliteColorsViolet Through Slighty Violetish Blue, Rarely ColorlessAlternateNamesCordierite, Dichroite, Bloodshot IoliteGemstoneGroupsKeySeparationsvisible pleochroism, refractive index, birefringence and optic character. Eye visible pleochroism.ClassificationCommentsMisnomer: water sapphire.
Iolite chemistry & crystallographyChemicalNamemagnesium aluminum silicateChemicalFormulaMg2Al4Si5O18SynthesisCrystalSystemOrthorhombicChemistryClassificationSilicateNatureNaturalCrystallinityCrystallineChemistryComments
Iolite optical propertiesTransparencyTransparent - TranslucentDispersionStrength: moderate fire Value: 0.017OpticalCommentsRefractiveIndex1.542-1.551
Tolerance:(+0.045/-0.011)Birefringence0.008-0.012OpticCharacterBiaxialOpticSignNegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert
LWUV: InertCCFReactionPleochroismTrichroic, violet, colorless to yellow, and light grayish blue
Iolite characteristic physical propertiesHardness7-7.5CharacteristicCommentsStreakWhiteSpecificGravity2.56-2.66 Range:+/-0.05 Typical:2.61ToughnessFairInclusionsIolite is a type II clarity stone. Sometimes apatite, hematite, iron oxide, magnetite, mica and rutile, inclusions are seen. Bloodshot iolite is the adventuresent variety with red plate like hematite, iron oxide inclusions along with goethite.LusterVitreousStabilityFairFractureConchoidal, UnevenCleavageGood, in one direction, Poor, in two directions