Peridot Gemstone & Information | Gemopedia by JTV | Gemopedia™
August's birthstone, peridot, is a relatively inexpensive, beautiful gem with a pedigree dating back as far as early Egyptians. Among its accolades, peridot can count being a favorite among royals and clergy, used to adorn everything from a queen's crown to a knight's sword. Peridot jewels were actually among Cleopatra's beloved treasures, though she believed them to be emeralds, as gems were then classified solely by color. Prized for its all natural, unenhanced range of colors, peridot is the gem variety of olivine and exhibits colors ranging from golden lime greens to rich grass greens.
Green, Greenish Yellow, Brownish Green
Peridot classificationCommonNamePeridotSpeciesForsteriteVarietyColorsGreen, Greenish Yellow, Brownish GreenAlternateNamesChrysolite, HawaiiteGemstoneGroupsOlivineKeySeparationsrefractive index, birefringence, optic character, spectrum and possibly magnification. High birefringence results often in very visible doubling of back facets under magnification.ClassificationCommentsCrystal habit is commonly an orthorhombic prism with vertical rhombic faces and side pinacoids. Peridot is a member of the olivine isomorphous series with forsterite (magnesium silicate) and fayalite (iron silicate) as the end members. Misnomers: evening emerald or night emerald. August birthstone.
Peridot chemistry & crystallographyChemicalNamemagnesium iron silicateChemicalFormula(Mg,Fe)2SiO4SynthesisCrystalSystemOrthorhombicChemistryClassificationSilicateNatureNaturalCrystallinityCrystallineChemistryComments
Peridot optical propertiesTransparencyTransparentDispersionOpticalCommentsRefractiveIndex1.654-1.69
Tolerance:(+0.020/-0.020)Birefringence0.035-0.038OpticCharacterBiaxialOpticSignPositive or NegativePolariscopeReactionDoubly Refractive (DR)FluorescenceSWUV: Inert
LWUV: InertCCFReactionPleochroismDichroic, unobservable or weak, varying shades of body color
Peridot characteristic physical propertiesHardness6.5-7CharacteristicCommentsStreakWhiteSpecificGravity3.27-3.38 Range:0.04/-0.07 Typical:3.34ToughnessVariesInclusionsPeridot is a type II clarity stone. Peridot might contain black octahedral chromite crystals. Stones might have liquid and gas inclusions that sometimes cause stress cracks that have a disk-like or "lily pad" appearance. Stones occasionally have mica flakes that give the stone a brownish hue. Stones from Pakistan often contain black ludwigite inclusions that have a hair or rod-like appearance.LusterVitreousStabilityFairFractureConchoidalCleavageGood, in two directions