Obsidian Gemstone & Information | Gemopedia by JTV | Gemopedia™

Obsidian

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.

Colors

Gray To Black, Brown To Brownish Yellow, Orange, Red. Rarely Blue, Green, Purple.

  • Obsidian classification

    CommonName
    Obsidian
    Species
    NA
    Variety
    Colors
    Gray To Black, Brown To Brownish Yellow, Orange, Red. Rarely Blue, Green, Purple.
    AlternateNames
    Banded Obsidian, Onyx Obsidian, Sheen Obsidian, Snowflake Obsidian, Rainbow Obsidian, Apache Tears
    GemstoneGroups
    KeySeparations
    RI, SG magnification and appearence
    ClassificationComments
    Natural glass; Misnomers: fire pearl, agni mani, glass agate, Montana jet, mountain jet, mountain mahogany, Nevada diamond, Nevada topaz, tokaylux sapphire, Iceland agate
  • Obsidian chemistry & crystallography

    ChemicalName
    silica
    ChemicalFormula
    SiO2(MgO,Fe3O4)
    Synthesis
    CrystalSystem
    NA
    ChemistryClassification
    Nature
    Natural
    Crystallinity
    Amorphous
    ChemistryComments
  • Obsidian optical properties

    Transparency
    Transparent - Opaque
    Dispersion
    Strength: weak fire Value: 0.01
    OpticalComments
    RefractiveIndex
    1.49
    Tolerance:(+0.020/-0.010)
    Birefringence
    OpticCharacter
    NA
    OpticSign
    NA
    PolariscopeReaction
    Singly Refractive (SR) With ADR
    Fluorescence
    SWUV: Inert
    LWUV: Inert
    CCFReaction
    Pleochroism
    None
  • Obsidian characteristic physical properties

    Hardness
    5-5.5
    CharacteristicComments
    Streak
    White
    SpecificGravity
    2.33-2.6 Typical:2.4
    Toughness
    Varies
    Inclusions
    Obsidian 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.
    Luster
    Vitreous
    Stability
    Fracture
    Conchoidal
    Cleavage
    None