Onyx Gemstone & Information | Gemopedia by JTV | Gemopedia™

Onyx

Onyx is the dark brown to black variety of agate, a cryptocrystalline quartz. Since ancient times onyx has afforded gem cutters and carvers an excellent source for carving cameos, intaglios and other jewelry creations. Inexpensive, abundant and available in large sizes, onyx is also a favored stone when fashioning cabochon gems and beads.

Colors

Black, White In Alternating Layers

  • Onyx classification

    CommonName
    Onyx
    Species
    Quartz
    Variety
    Chalcedony
    Colors
    Black, White In Alternating Layers
    AlternateNames
    True Onyx, Arabic Onyx
    GemstoneGroups
    KeySeparations
    RI, SG and appearance
    ClassificationComments
    Sometimes dyed and sold as black onyxSardonyx is different from onyx and is characterized by its carnelian or sard body color.
  • Onyx chemistry & crystallography

    ChemicalName
    silicon dioxide (aka silica)
    ChemicalFormula
    SiO2
    Synthesis
    CrystalSystem
    Trigonal
    ChemistryClassification
    Silicate
    Nature
    Natural
    Crystallinity
    Polycrystalline
    ChemistryComments
  • Onyx optical properties

    Transparency
    Semitransparent - Translucent
    Dispersion
    Strength: none
    OpticalComments
    RefractiveIndex
    1.535-1.539
    Birefringence
    0.004-0.004
    OpticCharacter
    Uniaxial
    OpticSign
    Positive
    PolariscopeReaction
    Aggregate (AGG)
    Fluorescence
    SWUV: Inert
    LWUV: Inert
    CCFReaction
    Pleochroism
    None
  • Onyx characteristic physical properties

    Hardness
    6.5-7
    CharacteristicComments
    Streak
    White
    SpecificGravity
    2.55-2.7 Typical:2.6
    Toughness
    Excellent
    Inclusions
    Onyx will have straight parallel layers of different colors.
    Luster
    Vitreous
    Stability
    Good
    Fracture
    Conchoidal, Granular
    Cleavage
    None