Andalusite Gemstone & Information | Gemopedia by JTV | Gemopedia™
Andalusite, an aluminum silicate, derives its name from the southern Spanish province of Andalusia, long believed to be the sight of its original discovery. Many now feel the original find may have actually occurred in El Cardoso, a different province in Spain, but the name endured. While andalusite's color play has been compared to alexandrite, this is technically incorrect, as it is pleochroic rather than color changing. Prized for its strong pleochroism, it displays different colors in different directions and features all its colors at once, whereas true color-change gems like alexandrite only change color when exposed to different light sources.
Yellowish Green To Brownish Green, Orangy Brown
Andalusite classificationCommonNameAndalusiteSpeciesAndalusiteVarietyColorsYellowish Green To Brownish Green, Orangy BrownAlternateNamesViridine, ChiastoliteGemstoneGroupsKeySeparationsPleochroism is usually evident from general observation. Identity may be confirmed by refractive index, birefringence, and optic character.ClassificationCommentsAndalusite is a polymorph of Al2SiO5 along with kyanite and sillimanite. Misnomers: poor man's alexandrite. Viridine is the dark green variety containing iron and manganese. Chiastolite is translucent to opaque and displays a cross.
Andalusite chemistry & crystallographyChemicalNamealuminum silicateChemicalFormulaAl2SiO5SynthesisCrystalSystemOrthorhombicChemistryClassificationSilicateNatureNaturalCrystallinityCrystallineChemistryComments
Andalusite optical propertiesTransparencyTransparent - OpaqueDispersionStrength: weak fire Value: 0.016OpticalCommentsRefractiveIndex1.634-1.643
Tolerance:(+0.005/-0.005)Birefringence0.007-0.013OpticCharacterBiaxialOpticSignNegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert to moderate green to yellowish green
LWUV: InertCCFReactionPleochroismTrichroic, strong yellowish green, green and brownish red
Andalusite characteristic physical propertiesHardness7.5CharacteristicCommentsStreakWhiteSpecificGravityTypical:3.17ToughnessVariesInclusionsAndalusite is a type II clarity stone. The needles or crystals seen in the stone are most likely rutile and apatite.LusterVitreousStabilityGoodFractureUnevenCleavageGood, in one direction, Poor, in one direction