|A variety or type of:||Chalcedony, which is a variety of Quartz|
Iris Agate - An iridescent variety of Agate.
Onyx - A monochromatic Agate with black and white banding.
Sardonyx - A monochromatic Agate with red/brown and either black or white banding.
|Photos of natural/un-cut material from mindat.org|
|Much agate is dyed to give strong and commercially acceptable colours. The material is sawn and shaped before dyeing. Immersion in a hot sugar solution followed by immersion in concentrated sulphuric acid and heating gives black; a blue colour, once called Swiss lapis, is produced by immersion in potassium ferrocyanide and subsequent warming in a solution of ferrous sulphate to give a precipitate of Berlin blue. Chromium alum or potassium dichromate may be used to give green or|
bluish green, and nickel compounds give a brighter, apple green. Impregnation with iron compounds and heating may give reddish brown and red colours. Yellow to greenish yellow is obtained by heating dry agate that has been treated with concentrated hydrochloric acid.
|Physical Properties of Agate|
|Mohs Hardness||6.5 to 7Blue Chart Gem Identification (2010) ,|
|Specific Gravity||2.60 to 2.64Gemstones of the world (2001) , More from other references|
|Cleavage Quality||NoneGemstones of the world (2001) ,|
|Fracture||UnevenGemstones of the world (2001) ,|
|Optical Properties of Agate|
|Refractive Index||1.530 to 1.543Blue Chart Gem Identification (2010) ,|
|Optical Character||Uniaxial/+Gemmological Tables (2004) , More from other references|
|Birefringence||up to to 0.004Gemstones of the world (2001) , More from other references|
|Pleochroism||AbsentGemstones of the world (2001) ,|
|Dispersion||NoneGemstones of the world (2001) ,|
|Colour (General)||Banding of different colours. Colours are generally pale though varied; natural colours are green, yellow, red, reddish brown, white and bluish white, among others.Gems, Sixth Edition (2006) ,|
|Transparency||Translucent,OpaqueGemmological Tables (2004) , More from other references|
|Lustre||WaxyManagement Team (2012) ,|
|Fluorescence & other light emissions|
|Fluorescence (General)||Varies with bands: partly strong; yellow, blue-whiteGemstones of the world (2001) ,|
|Crystallography of Agate|
|Crystal System||TrigonalManagement Team (2012) ,|
|Habit||Microcrystalline aggregatesGemstones of the world (2001) , More from other references|
|Where found:||It occurs in filling cavities, and individual bands are concentric to the external surface of the mass or nodule. Agate geodes are found in basic lavas and other igneous flow rocks and have probably been formed by silica deposition in cavities created by gases.Gems, Sixth Edition (2006) ,|
|Mineral information:||Agate information at mindat.org|
|Significant Gem Localities|