Alexandrite Gemstone & Information | Gemopedia by JTV | Gemopedia™
Alexandrite is the rare color-change variety of the mineral chrysoberyl. Its rarity is a result of its unlikely chemical makeup. Alexandrite can only form when aluminum and beryllium combine with trace elements like iron, titanium and, most importantly, chromium. On rare occasion, vanadium may also be present. The unlikelihood of the rare element chromium being in the right place to combine with aluminum and beryllium under exactly the right conditions to create alexandrite is what makes it so rare and valuable.
In Incandescent Light: Orangy, Brownish Red To Purplish Red; In Fluorescent, Daylight: Yellowish, Brownish, Grayish, Bluish Green
Alexandrite classificationCommonNameAlexandriteSpeciesChrysoberylVarietyAlexandriteColorsIn Incandescent Light: Orangy, Brownish Red To Purplish Red; In Fluorescent, Daylight: Yellowish, Brownish, Grayish, Bluish GreenAlternateNamesGemstoneGroupsKeySeparationsColor change, refractive index, birefringence, pleochroism and spectrumClassificationCommentsAlexandrite's spectrum varies by direction, showing a different spectrum in the green direction than in the purple-red pleochroic direction. Green, blue-green to pale green, yellowish, brownish, grayish in daylight or fluorescent light and violet, purplish to red, orangy or brownish in incandescent light.
Alexandrite chemistry & crystallographyChemicalNameberyllium aluminum oxideChemicalFormulaBeAl2O4SynthesisCrystalSystemOrthorhombicChemistryClassificationOxideNatureNaturalCrystallinityCrystallineChemistryComments
Alexandrite optical propertiesTransparencyTransparentDispersionStrength: weak fire Value: 0.015OpticalCommentsRefractiveIndex1.746-1.755
Tolerance:(+0.004/-0.006)Birefringence0.008-0.01OpticCharacterBiaxialOpticSignPositivePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: inert to moderate red
LWUV: inert to moderate redCCFReactionredPleochroismTrichroic, strong green, orange and purplish red
Alexandrite characteristic physical propertiesHardness8.5CharacteristicCommentsStreakWhiteSpecificGravity3.71-3.75 Range:+/- 0.02 Typical:3.73ToughnessVariesInclusionsAlexandrite is a type II clarity stone. The stone may contain fluorite, apatite, mica platlets, rutile and multi-phase inclusions along with negative crystals, fingerprints, liquid inclusions, needles and hollow tubes. Alexandrite's might show twinning.LusterBright VitreousStabilityVery GoodFractureConchoidalCleavageGood, in one direction