Staurolite (twinned) Gemstone & Information | Gemopedia by JTV | Gemopedia™
The name staurolite comes from the Greek word stauros, meaning cross. Staurolite is prized for its twinned crystals that intersect at 60 or 90 angles forming x-like or perpendicular crosses and specimens exhibiting these forms are highly prized by collectors. Sometimes referred to respectively as St. Andrew's and Greek crosses as well as lucky cross, fairy stone or fairy cross, one legend says the crystal crosses were created by the tears of fairies whom could not help but cry when they heard of Christ's crucifixion. Staurolite is a metamorphic mineral that ranges from translucent to opaque in appearance and facetable gems are vary rare.
Opaque Brown To Black
Staurolite-twinned classificationCommonNameStaurolite (twinned)SpeciesStauroliteVarietyStaurolite CrystalColorsOpaque Brown To BlackAlternateNamesCross Stones, Fairy CrossesGemstoneGroupsKeySeparationsAppearance of twins, RI and birefringenceClassificationCommentsTwinned crystals are 90o or 60o from each other
Staurolite-twinned chemistry & crystallographyChemicalNameiron aluminum silicate hydroxideChemicalFormula(Fe,Mg,Zn)2Al9(Si,Al)4O22(OH)2SynthesisCrystalSystemMonoclinicChemistryClassificationSilicateNatureNaturalCrystallinityAggregateChemistryComments
Staurolite-twinned optical propertiesTransparencyOpaqueDispersionOpticalCommentsRefractiveIndex1.736-1.746
Tolerance:(+0.015/-0.015)Birefringence0.009-0.015OpticCharacterBiaxialOpticSignPositivePolariscopeReactionAggregate (AGG)FluorescenceSWUV: Inert
Staurolite-twinned characteristic physical propertiesHardness7-7.5CharacteristicCommentsStreakWhiteSpecificGravity3.65-3.79 Typical:3.71ToughnessFairInclusionsLusterVitreousStabilityFractureConchoidal, UnevenCleavageGood, in one direction