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colorless, white, gray, ...
Waxy, Dull
6½ - 7
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 for gemological information about Chalcedony.

Classification of Chalcedony

Physical Properties of Chalcedony

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

Optical Data of Chalcedony

Uniaxial (+)

Chemical Properties of Chalcedony

Elements listed in formula:
Analytical Data:
More soluble in water and more easily attacked by alkaline solutions than macrocrystalline quartz.

Occurrences of Chalcedony

First Recorded Occurrence of Chalcedony

Relationship of Chalcedony to other Species

Other Names for Chalcedony

Name in Other Languages:
Norwegian (Bokmål):Kalsedon
Serbian (Cyrillic Script):Калцедон
Simplified Chinese:玉髓

Other Information

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 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 petrology

An essential component of (items highlighted in red)

References for Chalcedony

Reference List:
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.

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Localities for Chalcedony

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