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Chalcedony
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Byšta, Trebišov Co., Košice Region, Slovakia
© Albert Russ
| System: | Trigonal | Colour: | colorless, white, gray, ... |
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| Hardness: | 6½ - 7 |
A variety of Quartz
Traditionally defined as a fibrous cryptocrystalline variety of Quartz, more recently, it has been shown that much Chalcedony is a mixture of Quartz and Mogánite, another silica mineral. Pure chalcedony may contain trace amounts of silanol (OH) groups (Schmidt et al., 2012).
When it is concentrically banded (often in rather wild patterns) it is called by the subvariety name Agate. When it is in flat layers/bands it is called by the subvariety name Onyx.
[Note: Many non-banded forms of chalcedony - such as Moss agate - are often erroneously called 'agates'. True agate is concentrically banded. Mottled and included chalcedonies are more properly called simply 'chalcedony.' Petrified wood (agatized wood) is the name given to fossil wood where the replacement of the wood is by chalcedony, but the banding in this case is due to the wood structure - not concentric deposition of the chalcedony - and the material is chalcedony, not true agate.]
Chalcedony: Agate, Mexico
Chalcedony: Chalcedony Rose, New Mexico
Chalcedony: Red Jasper, Arizona
Chalcedony: Flint Nodule, England
Chalcedony: Chrysoprase, Poland
Chalcedony: Heliotrope, Brazil
Visit gemdat.org for gemological information about Chalcedony. Currently in public beta-test.
Traditionally defined as a fibrous cryptocrystalline variety of Quartz, more recently, it has been shown that much Chalcedony is a mixture of Quartz and Mogánite, another silica mineral. Pure chalcedony may contain trace amounts of silanol (OH) groups (Schmidt et al., 2012).
When it is concentrically banded (often in rather wild patterns) it is called by the subvariety name Agate. When it is in flat layers/bands it is called by the subvariety name Onyx.
[Note: Many non-banded forms of chalcedony - such as Moss agate - are often erroneously called 'agates'. True agate is concentrically banded. Mottled and included chalcedonies are more properly called simply 'chalcedony.' Petrified wood (agatized wood) is the name given to fossil wood where the replacement of the wood is by chalcedony, but the banding in this case is due to the wood structure - not concentric deposition of the chalcedony - and the material is chalcedony, not true agate.]
Chalcedony: Agate, Mexico
Chalcedony: Chalcedony Rose, New Mexico
Chalcedony: Red Jasper, Arizona
Chalcedony: Flint Nodule, England
Chalcedony: Chrysoprase, Poland
Chalcedony: Heliotrope, Brazil
Visit gemdat.org for gemological information about Chalcedony. Currently in public beta-test.
Classification of Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| mindat.org URL: | http://www.mindat.org/min-960.html Please feel free to link to this page. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Physical Properties of Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Lustre: | Waxy, Dull | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Diaphaneity (Transparency): | Translucent | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Comment: | vitreous when polished | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Colour: | colorless, white, gray, blue, any color due to embedded minerals, multicolored specimen not uncommon. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Streak: | White | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Hardness (Mohs): | 6½ - 7 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Tenacity: | Brittle | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cleavage: | None Observed | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fracture: | Conchoidal | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Density (measured): | 2.6 g/cm3 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Comment: | varies with amount and type of impurities | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Crystallography of Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Crystal System: | Trigonal | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Other Names for Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Synonyms: |
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Other Information | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fluorescence in UV light: | None in pure specimen, however green fluorescence in short-wave UV light is very common at many localities. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other Information: | Certain sub-varieties like jasper may be opaque. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Health Warning: | No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
References for Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Reference List: - + | Flörke, O.W. et al. (1991) Nomenclature of micro- and non-crystalline silica minerals based on structure and microstructure. Neues Jahrbuch Miner. Abh., Vol 163, 19-42 Graetsch, H. (1994) Structural characteristics of opaline and microcrystalline silica minerals. Reviews in Mineralogy, Vol.29, Silica - Physical behavior, geochemistry and materials applications. Patrick Schmidt, Ludovic Bellot-Gurlet, Aneta Slodczyk, François Fröhlich (2012): A hitherto unrecognised band in the Raman spectra of silica rocks: influence of hydroxylated Si–O bonds (silanole) on the Raman moganite band in chalcedony and flint (SiO2). Physics and Chemistry of Minerals 39, 455-464. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mindat.org articles about Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Internet Links for Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Specimens: | The following Chalcedony specimens are currently listed for sale on minfind.com. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Localities for Chalcedony | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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The map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the
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