Agate gemstone information (original) (raw)
India
14.62 carats
© gemselect.com
Agate is a banded, concentric shell-like Chalcedony, sometimes containing opal substance. The bands can be multicoloured or of the same colour.
Originally reported from Dirillo river (Achates river), Acate, Ragusa Province, Sicily, Italy.
Agate Gemstones by Colour
This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
Agate Gemstones by Size
This table shows distribution of Agate gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
0.90ct to 36.42ct36.42ct to 71.94ct71.94ct to 107.46ct107.46ct to 142.98ct142.98ct to 178.50ct178.50ct to 214.02ct214.02ct to 249.54ct249.54ct to 285.06ct285.06ct to 320.58ct320.58ct to 356.10ct
| General Information | |
|---|---|
| A variety or type of: | Chalcedony, which is a variety of Quartz |
| Varieties/Types: | 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. |
| Chemical Formula | SiO 2, Gemmological Tables (2004) |
| Agate Treatments | |
| 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 orbluish 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 7Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) |
| Specific Gravity | 2.60 to 2.64Walter Schumann, Gemstones of the world (2001) More from other references |
| Cleavage Quality | NoneWalter Schumann, Gemstones of the world (2001) |
| Fracture | UnevenWalter Schumann, Gemstones of the world (2001) |
| Optical Properties of Agate | |
| Refractive Index | 1.530 to 1.543Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) |
| Optical Character | Uniaxial/+Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
| Birefringence | up to to 0.004Walter Schumann, Gemstones of the world (2001) More from other references |
| Pleochroism | AbsentWalter Schumann, Gemstones of the world (2001) |
| Dispersion | NoneWalter Schumann, Gemstones of the world (2001) |
| Colour | |
| 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.Michael O?Donoghue, Gems, Sixth Edition (2006) |
| Transparency | Translucent,OpaqueUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) More from other references |
| Lustre | Waxygemdat.org, Management Team (2012) |
| Fluorescence & other light emissions | |
| Fluorescence (General) | Varies with bands: partly strong; yellow, blue-whiteWalter Schumann, Gemstones of the world (2001) |
| Crystallography of Agate | |
| Crystal System | Trigonalgemdat.org, Management Team (2012) |
| Habit | Microcrystalline aggregatesWalter Schumann, Gemstones of the world (2001) More from other references |
| Geological Environment | |
| 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.Michael O?Donoghue, Gems, Sixth Edition (2006) |
| Further Information | |
| Mineral information: | Agate information at mindat.org |
| Significant Gem Localities | |
| Brazil **Rio Grande do Sul**Peru Huancavelica Huancavelica Province Ascencion District Yauricocha Parish YanacodoUK Scotland Angus Montrose Usan Blue Hole[Specimen in the Natural History Museum, London]USA California Siskiyou County Klamath Mountains Cinnabar Camp Unnamed Gemstone occurrence [1]U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia. Utah Juab County Thomas Range Topaz Mountain Unnamed Agate depositU.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia. |