Obsidian Gemstone & Information | Gemopedia by JTV | Gemopedia™
Obsidian is formed by the rapid cooling of viscous lava due to volcanic explosions. It consists of the same minerals as granite, but cools so quickly that they do not have time to crystallize. Obsidian has a glassy luster and is usually black or a very dark green, but it can also be found in an almost colorless form.
Gray To Black, Brown To Brownish Yellow, Orange, Red. Rarely Blue, Green, Purple.
Obsidian classificationCommonNameObsidianSpeciesNAVarietyColorsGray To Black, Brown To Brownish Yellow, Orange, Red. Rarely Blue, Green, Purple.AlternateNamesBanded Obsidian, Onyx Obsidian, Sheen Obsidian, Snowflake Obsidian, Rainbow Obsidian, Apache TearsGemstoneGroupsKeySeparationsRI, SG magnification and appearenceClassificationCommentsNatural glass; Misnomers: fire pearl, agni mani, glass agate, Montana jet, mountain jet, mountain mahogany, Nevada diamond, Nevada topaz, tokaylux sapphire, Iceland agate
Obsidian chemistry & crystallographyChemicalNamesilicaChemicalFormulaSiO2(MgO,Fe3O4)SynthesisCrystalSystemNAChemistryClassificationNatureNaturalCrystallinityAmorphousChemistryComments
Obsidian optical propertiesTransparencyTransparent - OpaqueDispersionStrength: weak fire Value: 0.01OpticalCommentsRefractiveIndex1.49
Tolerance:(+0.020/-0.010)BirefringenceOpticCharacterNAOpticSignNAPolariscopeReactionSingly Refractive (SR) With ADRFluorescenceSWUV: Inert
Obsidian characteristic physical propertiesHardness5-5.5CharacteristicCommentsStreakWhiteSpecificGravity2.33-2.6 Typical:2.4ToughnessVariesInclusionsObsidian often has gas bubbles, cristobalite inclusions and stubby needle like inclusions. Banded obsidian: curved or sinuous bandsMacusanite: pale yellow to greenish obsidian from Peru. Mahogany obsidian: red and black banded material. Onyx obsidian: straight, parallel bandsSheen obsidian: silvery or golden looking sheen caused by gas bubbles Snowflake or flowering obsidian: white patches of cristobalite inclusions on a black backgroundRainbow obsidian: rainbow iridescent colors caused by numerous tiny bubblesApache tears: small, rounded irregularly shaped black nodules found in the American Southwest.LusterVitreousStabilityFractureConchoidalCleavageNone