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Chalcedony

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System:TrigonalColour:colorless, white, gray, ...
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


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Classification of Chalcedony

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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:
CeracahtesCerachatesChalcedoneChalcedoniteChalcedononyx
Merlinite
Other Languages:
Basque:Kaltzedonia
Breton:Kalkedon
Catalan:Calcedònia
Czech:Chalcedon
Dutch:Chalcedoon
Esperanto:Kalcedono
Estonian:Kaltsedon
Finnish:Kalsedoni
French:Calcédoine
German:Chalcedon
Chalcedonit
Chalzedon
Kalzedon
Hebrew:כלקדון
Italian:Calcedonio
Japanese:石髓
Korean:옥수
Latin:Calcedonius
Latvian:Halcedons
Lithuanian:Chalcedonas
Norwegian (Bokmål):Kalsedon
Polish:Chalcedon
Portuguese:Calcedônia
Romanian:Calcedon
Russian:Халцедон
Serbian (Cyrillic Script):Калцедон
Simplified Chinese:玉髓
Slovak:Chalcedón
Spanish:Calcedonia
Swedish:Kalcedon
Turkish:Kalsedon
Ukrainian:Халцедон
Varieties:
Abakusz-köAgateAgate-JasperAgatized coralAmarillo Stone
AmberineAzurchalcedonyBall JasperBasaniteBayate
BeekiteBinghamiteBloodstoneBlue ChalcedonyBlue Lace Agate
Botswana AgateBrecciated AgateBuhrstoneCarnelianChrome-Chalcedony
ChrysojasperCloud AgateCrazy Lace AgateCreoliteCubosilicite
DallasiteDamsoniteDarlingiteDendritic AgateDiackethyst
Egyptian JasperEnhydro AgateEye AgateFairburn AgateFire Agate
Fortification AgateFossil AgateHaema-ovoid-agatesHerbeckiteIris Agate
IrnimiteJasperKeystonite ChalcedonyKinraditeLaguna Agate
Lake Superior AgateLandscape AgateMexican Lace AgateMocha StoneMoss Agate
MyrickiteNipomo AgateOnyxOrbicular JasperOwyhee Jasper
PastelitePietersitePigeon Blood AgatePlasmaPlume Agate
QuartzineQuetzalitztliRiband AgateRiband JasperSard
SardonyxSchlangenhautachatSeftoniteSnakeskin AgateVogelaugenachat
VogelaugenjaspisWatercolour jasperWilkiteYoungite

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

Article entries:
Boley agatesDavid Goza

Internet Links for Chalcedony

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