Oligoclase Gemstone & Information | Gemopedia by JTV | Gemopedia™

Oligoclase is a member of the plagioclase feldspar group. Two oligoclase varieties, sunstone and moonstone, are prized for their phenomenal optical properties.
Colors
Yellow, Brown To Orange, Brownish Red, Colorless, White To Light Green, Gray
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Oligoclase classification
CommonNameOligoclaseSpeciesOligoclaseVarietyColorsYellow, Brown To Orange, Brownish Red, Colorless, White To Light Green, GrayAlternateNamesGemstoneGroupsFeldsparKeySeparationsappearance, RI, birefringence and optic character.ClassificationCommentsIf adventurescence is present then the stone is sunstone. -
Oligoclase chemistry & crystallography
ChemicalNamecalcium or sodium silicateChemicalFormulaNaAlSi3O8 or CaAl2Si2O8SynthesisCrystalSystemTriclinicChemistryClassificationSilicateNatureNaturalCrystallinityCrystalline to AggregateChemistryComments -
Oligoclase optical properties
TransparencyTranslucent - OpaqueDispersionOpticalCommentsRefractiveIndex1.539-1.547
Tolerance:(+0.004/-0.006)Birefringence0.007-0.01OpticCharacterBiaxialOpticSignNegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert
LWUV: InertCCFReactionPleochroismUnobservable -
Oligoclase characteristic physical properties
Hardness6-6.5CharacteristicCommentsStreakSpecificGravity2.62-2.67 Typical:2.65ToughnessPoorInclusionsOligoclase feldspar has parallel closely spaced twinning planes. Transparent material might show eye-visible iridescent platelets.LusterVitreousStabilityGoodFractureUneven, SplinteryCleavagePerfect, in two directions