Agate Gemstone & Information | Gemopedia by JTV | Gemopedia™
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.
Almost All Colors
Agate classificationCommonNameAgateSpeciesQuartzVarietyChalcedonyColorsAlmost All ColorsAlternateNamesGemstoneGroupsKeySeparationsAppearance, fracture, refractive index, specific gravityClassificationCommentsAgate 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 & crystallographyChemicalNamesilicon dioxide (aka silica)ChemicalFormulaSiO2SynthesisCrystalSystemTrigonalChemistryClassificationSilicateNatureNaturalCrystallinityPolycrystallineChemistryComments
Agate optical propertiesTransparencySemitransparent - TranslucentDispersionStrength: noneOpticalCommentsRefractiveIndex1.535-1.539Birefringence0.004-0.004OpticCharacterNAOpticSignNAPolariscopeReactionAggregate (AGG)FluorescenceSWUV: Inert
Agate characteristic physical propertiesHardness6CharacteristicCommentsStreakSpecificGravity2.55-2.7 Typical:2.6ToughnessExcellentInclusionsTypical 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.LusterGreasyStabilityGoodFractureConchoidal, GranularCleavageNone