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Chalcedony

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Formula:
SiO2
Colour:
colorless, white, gray, blue, any color due to embedded minerals, multicolored specimen not uncommon.
Lustre:
Waxy, Dull
Hardness:
6½ - 7
Specific Gravity:
2.6
Name:
Mentioned by Agricola (1546) of a stone named for the town of Chalcedon, now called Kadıköy, and is a district within the city of Istanbul, Turkey.
A variety of Quartz

Depending on the context, the term "chalcedony" has different meanings.

1. A more general term for all varieties of quartz that are made of microscopic or submicroscopic crystals, the so-called microcrystalline varieties of quartz. Examples are the different types of agate, jasper, chert, chrysoprase, onyx, pietersite, etc.


2. In the strict sense, and in scientific literature, "chalcedony" designates aggregates of parallely grown ("fibrous") quartz crystals of microscopic and sub-microscopic size. Based on the conspicious behaviour of thin sections of chalcedony in polarized light, at least two types can be distinguished (Michel-Lévy and Munier-Chalmas, 1892; Correns and Nagelschmidt, 1933; Braitsch, 1957; Frondel, 1978; Flörke et al. 1991):
- length-fast chalcedony, with crystallites stacked perpendicular to the c-axis, and the resulting fibers being elongated either along [1120] or -more rarely - along [1010]. The fibers may be twisted around the elongation axis.
- length-slow chalcedony or Quartzine, with crystallites stacked parallel to the c-axis, and the resulting fibers being elongated along [0001], like in macrocrystalline quartz.

Both types tend to develop radially grown "fibers", resulting in botryoidal, rounded and stalactitic habits. They often show concentric banding perpendicular to the fiber orientation and are then called Agate.
Length-fast chalcedony and quartzine may be found intergrown. The crystallites are commonly polysynthetically twinned by the Brazil law (Graetsch, 1994; Cady et al 1998; Xu et al 1998).
It is not possible to distinguish the types with the naked eye. Length-fast chalcedony is far more common than quartzine.

Aggregates of randomly intergrown microscopic grains are called "microquartz" (Flörke et al, 1991; Graetsch, 1994). The more general term explained under (1) includes length-slow and length-fast chalcedony as well as microquartz.

Most chalcedony contains small amounts of the silica mineral Mogánite, usually between 1% and 20% (Heaney and Post, 1992). Aging slowly converts the mogánite into quartz and results in mogánite-free chalcedony (Moxon, 2004) .
Chalcedony contains small amounts of water, both as molecular water and bound in silanole (Si-OH) groups (Frondel, 1982).


3. A term sometimes used for chalcedony that is not agate, jasper or another sub-variety. Used in particular for botryoidal specimens.



Chalcedony: Agate, Mexico
Chalcedony: Chalcedony Rose, New Mexico
Chalcedony: Red Jasper, Arizona
Chalcedony: Agate, Mexico
Chalcedony: Chalcedony Rose, New Mexico
Chalcedony: Red Jasper, Arizona
Chalcedony: Agate, Mexico
Chalcedony: Chalcedony Rose, New Mexico
Chalcedony: Red Jasper, Arizona
Chalcedony: Flint Nodule, England
Chalcedony: Chrysoprase, Poland
Chalcedony: Heliotrope, Brazil
Chalcedony: Flint Nodule, England
Chalcedony: Chrysoprase, Poland
Chalcedony: Heliotrope, Brazil
Chalcedony: Flint Nodule, England
Chalcedony: Chrysoprase, Poland
Chalcedony: Heliotrope, Brazil




Visit gemdat.org for gemological information about Chalcedony.


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Physical Properties of ChalcedonyHide

Waxy, Dull
Transparency:
Translucent
Comment:
vitreous when polished, fractured surfaces have a dull or waxy luster
Colour:
colorless, white, gray, blue, any color due to embedded minerals, multicolored specimen not uncommon.
Streak:
White
Hardness:
6½ - 7 on Mohs scale
Tenacity:
Brittle
Cleavage:
None Observed
Less brittle than macrocrystalline quartz.
Fracture:
Conchoidal, Sub-Conchoidal
Density:
2.6 g/cm3 (Measured)    
Comment:
varies with amount and type of impurities

Optical Data of ChalcedonyHide

Type:
Uniaxial (+)
Pleochroism:
Non-pleochroic

Chemical Properties of ChalcedonyHide

Formula:
SiO2

First Recorded Occurrence of ChalcedonyHide

Synonyms of ChalcedonyHide

Other Language Names for ChalcedonyHide

Breton:Kalkedon
Catalan:Calcedònia
Czech:Chalcedon
Esperanto:Kalcedono
Estonian:Kaltsedon
Finnish:Kalsedoni
Italian:Calcedonio
Japanese:石髓
Korean:옥수
Latvian:Halcedons
Lithuanian:Chalcedonas
Norwegian (Bokmål):Kalsedon
Polish:Chalcedon
Portuguese:Calcedônia
Romanian:Calcedon
Serbian (Cyrillic Script):Калцедон
Simplified Chinese:玉髓
Slovak:Chalcedón
Spanish:Calcedonia
Swedish:Kalcedon
Turkish:Kalsedon

Varieties of ChalcedonyHide

AgateA distinctly banded fibrous chalcedony. Originally reported from Dirillo river (Achates river), Acate, Ragusa Province, Sicily, Italy.
Agate-JasperA variety of Agate consisting of Jasper veined with Chalcedony.
Agatized coralA variety of agate/chalcedony replacing coral.
Amarillo StoneA figured variety of chalcedony.
May be the same as Alibates flint.
AmberineYellow to yellow-green chalcedony variety found in Death Valley, Inyo Co., California, USA.
AquapraseA bluish green chalcedony, colored by chromium and nickel, is marketed under the trade name “Aquaprase.” Origin is an unspecified locality in Africa.
The colour is due to one or more Cr- and/or Ni-bearing phases on the grain boundaries of quartz.
AzurchalcedonyChalcedony coloured by Chrysocolla, from Arizona, USA
BeekiteA name given to Chalcedony pseudomorphs after coral or shells.
Originally described from Devon, England, UK.
BinghamiteChatoyant chalcedony included with dense and parallel fibres of Goethite and/or Hematite. Similar to Tiger's Eye.
Bird's Eye AgateA variety of eye agate where the eyes are supposed to resemble the eyes of a bird.
Blue Chalcedony
Blue Lace AgateA pale blue banded variety of Agate (Chalcedony).
Botswana AgateA variety of agate from Botswana, banded with fine, parallel lines, often coloured pink blending into white.
Brecciated AgateA naturally cemented matrix of broken agate fragments.
BuhrstoneA cellular flinty material used for millstones.
CarnelianA reddish variety of Chalcedony.
Chrome-ChalcedonyA variety of chalcedony colored deep green by Cr compounds. (Compare with the more common Chrysoprase variety of chalcedony, which is colored by nickel.) Chrome chalcedony found in an ancient Roman gem collection may have come from one of the chromium dep...
Cloud AgateGreyish agate with patches of blurry, foggy inclusions.
Crazy Lace AgateAn agate composed of multicoloured twisting and turning bands.
CubosilicitePseudomorphs of Chalcedonly after Fluorite - small blue cubes
DamsoniteTrade name for a light violet to dark purple chalcedony from Arizona.
Dendritic AgateChalcedony containing dendritic inclusions.
DiackethystA local name for translucent wine and amethystine coloured chalcedony pebbles.
Originally described from Craig, Montrose, Tayside (Angus), Scotland, UK.
Enhydro AgateAn agate nodule partly filled with water.
Eye AgateAgate with concentric ring pattern, looking like an eye.
Fairburn AgateA unique and rare variety of Fortification Agate from Fairburn, Custer Co., South Dakota, USA.
Fire AgateA variety of chalcedony containing inclusions of goethite or limonite, producing an iridescent effect or "fire."
Fortification AgateAgate with sharp-angled bands which resemble the outlines of fortifications of a castle.
Fossil AgateAgate as a replacement material in fossils.
Haema-ovoid-agatesName proposed for a reddish agate with ovoidal patches of cacholong, etc.
HerbeckiteA variety of Agate or Jasper impregnated with Iron Hydrate. [Clark, 1993 - "Hey's Mineral Index"]
Originally described from Hrbek Mine, Svatá Dobrotivá (St Benigna), Beroun (Beraun), Central Bohemia Region, Bohemia (Böhmen; Boehmen), Czech Republic.
Iris AgateAn iridescent variety of agate - when sliced into a thin section it exhibits all the colours of the spectrum when viewed in transmitted light.
Keystonite ChalcedonyA local trade name for Chalcedony coloured blue by Chrysocolla.
Laguna AgateA colourful agate variety.
Originally described from Ojo Laguna, Chihuahua, Mexico.
Lake Superior AgateBelieved to be the world's oldest agates, over 1 billion years old, these are found throughout the northern US having been spread from the original Lake Superior region by glaciation. It has generally pale colouring.
Landscape AgateA variety of chalcedony with inclusions giving the appearance of a landscape scene.
Mexican Lace AgateLacy or wavy agate from Mexico.
Mocha StoneA variety of agate (chalcedony) containing inclusions of pyrolusite.
Moss AgateA variety of Chalcedony frequently containing green mineral inclusions (eg Chlorite, Hornblende, etc.) or brown to black dendrites of iron or manganese oxides.
MyrickiteLocal name for Chalcedony with grey ground and red spots (cinnabar).
Nipomo AgateChalcedony with inclusions of Marcasite.
OnyxIn correct usage, the name refers to a black and white banded variety of Agate, or sometimes a monochromatic agate with dark and light bands (brown and white for example) - but traditionally the name was reserved for black and white banded agate, and brow...
PietersiteChalcedony with embedded fibers of amphibole minerals with varying degrees of alteration. Blue-gray, brown and yellow colors. The fibers cause a chatoyancy similar to that seen in tiger's eye, but tiger's eye is not made of chalcedony, it is macrocrystall...
Pigeon Blood AgateA blood-red and white variety of agate from Utah.
PlasmaA microgranular or microfibrous form of chalcedony coloured in various shades of green by disseminated silicate particles (variously attributed to celadonite, chlorite, amphibole, etc.).
Plume AgateA variety of chalcedony with contrasting colored, plume-like structures within the material.
QuartzineQuartzine is a fibrous variety of chalcedony. It is also called "length-slow chalcedony" and is usually intergrown with another, more common type of fibrous chalcedony, "length-fast chalcedony", that comprises most of the different varieties of chalcedony...
Riband AgateAccording to Hey's 3rd Ed. this is 'a banded agate', which doesn't tell us much!
SardA brown to brownish-red translucent variety of Chalcedony. Pliny the Elder stated that it was named after Sardis, in Lydia, where it was first discovered; but the name probably came with the stone from Persia (Pers. sered, yellowish-red).
SardonyxA variety of Agate with reddish-brown and either black or white bands.
SeftoniteA translucent, moss green variety of chalcedony.
Snakeskin AgateChalcedony with snakeskin-like surface pattern.
YoungiteLocal name for agate or jasper coated by druzy quartz crystals.
Found near Guernsey Wyoming in limestone rocks.

Common AssociatesHide

CalciteCaCO3
Goethiteα-Fe3+O(OH)
HematiteFe2O3
OpalSiO2 · nH2O
QuartzSiO2
Zeolite GroupA group name for a large number of framework alumosilicates (and, rarely, beryllosilicates, zincosilicates, ...
Associated Minerals Based on Photo Data:
Quartz453 photos of Chalcedony associated with Quartz on mindat.org.
Calcite272 photos of Chalcedony associated with Calcite on mindat.org.
Amethyst109 photos of Chalcedony associated with Amethyst on mindat.org.
Fluorite86 photos of Chalcedony associated with Fluorite on mindat.org.
Siderite83 photos of Chalcedony associated with Siderite on mindat.org.
Stibnite71 photos of Chalcedony associated with Stibnite on mindat.org.
Stilbite-Ca67 photos of Chalcedony associated with Stilbite-Ca on mindat.org.
Stilbite64 photos of Chalcedony associated with Stilbite on mindat.org.
Pyrite56 photos of Chalcedony associated with Pyrite on mindat.org.
Fluorapophyllite-(K)48 photos of Chalcedony associated with Fluorapophyllite-(K) on mindat.org.

Fluorescence of ChalcedonyHide

None in pure specimen, however green fluorescence in short-wave UV light is very common at many localities.

Other InformationHide

Notes:
Certain sub-varieties like jasper may be opaque.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Chalcedony in petrologyHide

An essential component of (items highlighted in red)

References for ChalcedonyHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Michel-Lévy, A., Munier-Chalmas, C.P.E. (1892) Mémoire sur diverses formes affectées par le réseau élémentaire du quartz. Bulletin de la Société Française de Minéralogie: 15: 159-190.
Correns, C.W., Nagelschmidt, G. (1933) Über Faserbau und optische Eigenschaften von Chalzedon. Zeitschrift für Kristallographie: 85: 199-213.
Braitsch, O. (1957) Über die natürlichen Faser- und Aggregationstypen beim SiO2, ihre Verwachsungsformen, Richtungsstatistik und Doppelbrechung. Heidelberger Beiträge zur Mineralogie und Petrographie: 5: 331-372.
White, J.F., Corwin, J.F. (1961) Synthesis and origin of chalcedony. American Mineralogist: 46: 112-119.
Monroe, E.A. (1964) Electron optical observations of fine-grained silica minerals. American Mineralogist: 49: 339-347.
Maleev, M.N. (1972) Diagnostic features of spherulites formed by splitting of a single-crystal nucleus. Growth mechanism of chalcedony. Tschermaks Mineralogische und Petrographische Mitteilungen: 18: 1-16.
Frondel, C. (1978) Characters of quartz fibers. American Mineralogist: 63: 17-27.
Frondel, C. (1982) Structural hydroxyl in chalcedony (type B quartz). American Mineralogist: 67: 1248-1257.
Flörke, O.W., Graetsch, H., Martin, B., Röller, K., Wirth, R. (1991) Nomenclature of micro- and non-crystalline silica minerals based on structure and microstructure. Neues Jahrbuch für Mineralogie - Abhandlungen: 163: 19-42.
Gíslason, S.R., Heaney, P.J., Veblen, D.R., Livi, K.J.T. (1993) The difference between the solubility of quartz and chalcedony: the cause? Chemical Geology: 107: 363-366.
Graetsch, H. (1994) Structural characteristics of opaline and microcrystalline silica minerals. Reviews in Mineralogy, Vol.29, Silica - Physical behavior, geochemistry and materials applications.
Cady, S.L., Wenk, H.R., Sintubin, M. (1998) Microfibrous quartz varieties: characterization by quantitative X-ray texture analysis and transmission electron microscopy. Contributions to Mineralogy and Petrology: 130: 320-335.
Xu, H., Buseck, P.R., Luo, G. (1998) HRTEM investigation of microstructure in length-slow chalcedony. American Mineralogist: 83: 542-545.
Moxon, T. (2004) Moganite and water content as a function of age in agate: an XRD and thermogravimetric study. European Journal of Mineralogy: 16: 269-278.
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.
Götze, J., Gaft, M., Möckel, R. (2015) Uranium and uranyl luminescence in agate/chalcedony. Mineralogical Magazine: 79: 985-995.

Internet Links for ChalcedonyHide

Localities for ChalcedonyHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListShow