Agate Gemstone & Information | Gemopedia by JTV | Gemopedia™

Agate

Agate is the banded form of chalcedony, a cryptocrystalline variety of quartz. Rather than a single crystal, it is composed of a myriad of miniature crystals that can only be seen with extreme magnification. Agate's name is derived from the site of its discovery, the river Achates (now Dirillo) in southwest Sicily. You will often find striking curved or angular banded patterns of color flowing within agate, which are caused by the presence of various minerals, often iron and manganese. One of the oldest known gemstones, agate is a favored material of lapidaries and artisans around the world.

Colors

Almost All Colors

  • Agate classification

    CommonName
    Agate
    Species
    Quartz
    Variety
    Chalcedony
    Colors
    Almost All Colors
    AlternateNames
    GemstoneGroups
    KeySeparations
    Appearance, fracture, refractive index, specific gravity
    ClassificationComments
    Agate is a variety of chalcedony, a semitransparent to translucent polycrystalline quartz with curved, angular or gnarly bands or layers. "Agates form in nodules and veins in secondary container rocks" (Agates and Jaspers: Ron Gibbs). Typically carved or fashioned into beads, cabochons or sliced to show its banding. Dyeing is also sometimes employed for color or emphasis on the successive layers or bands. Fortification Agate: banded agate that is that have alternating parallel layers of varying colors. Plume Agate: has feathery appearance. Moss and Tube Agate: have a moss or tube like appearance. Sagenitic Agate: agates with secondary crystal replacements.
  • Agate chemistry & crystallography

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

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

    Hardness
    6
    CharacteristicComments
    Streak
    SpecificGravity
    2.55-2.7 Typical:2.6
    Toughness
    Excellent
    Inclusions
    Typical agate is described as having curved angular banding or layers, but it can also have a plume or moss like appearance. Bands may have a very fine grain or fibrous structure due to its microcrystalline structure and may vary in translucency. Agate is sometimes dyed.
    Luster
    Greasy
    Stability
    Good
    Fracture
    Conchoidal, Granular
    Cleavage
    None