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Chert

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Colour:Gray, white; black, ...Hardness:6½ - 7
Name:"Chert, perhaps originally chirt, is believed to be a local English term that was taken into geological use. It may be of onomatopoeic origin. The name chert may be of more recent origin than flint, and unlike flint, is not found in literary usage. It was well established in meaning in 1679 ..." (Frondel, C., 1962, The System of Mineralogy, v. 3, John Wiley & Sons, p. 223.)


A tough, dense rock composed of quartz and few other impurities. The quartz occurs as randomly interlocked, microscopic quartz grains (microquartz) or microscopic grains of fibrous chalcedony.

Chert forms layers and nodules, but also large beds in sedimentary and metamorphic rocks, occurs in epithermal veins, by direct deposition around submarine hydrothermal vents and may form as a product of silicification of biogenic or volcanogenic sediments. Chert of sedimentary origin often contains fossils.

The term "chert" is used for rocks mostly composed of quartz, siliceous precursor rocks of comparable texture are sometimes also called chert, but with the addition of the dominant silica phase, like "opaline chert".

Classification of Chert

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Physical Properties of Chert

Lustre:Waxy, Dull
Diaphaneity (Transparency):Translucent, Opaque
Colour:Gray, white; black, brown and other colors due to staining
Streak:White or lightly colored
Hardness (Mohs):6½ - 7
Tenacity:Brittle
Cleavage:None Observed
Fracture:Splintery, Conchoidal, Sub-Conchoidal

Other Names for Chert

Synonyms:
HornstoneMozarkite
Other Languages:
German:Mozarkit
Simplified Chinese:硅质岩
Spanish:Mozarkita
Varieties:
NovaculiteRibbonstoneTaconite

Other Information

Health Warning:Like all quartz, breathing in fine particles for a prolonged period will produce silicosis.

References for Chert

Reference List:

- +
Smith, W.E. (1960) The silicious constituents of chert. Geologie en Mijnbouw 39e, 1-8.

Hay, R.L. (1968) Chert and its sodium-silicate precursors in sodium-carbonate lakes of East Africa. Contributions to Mineralogy and Petrology 17, 255-274.

Oldershaw, A.E. (1968) Electron-microscopic examination of namurian bedded cherts, North Wales (Great Britain). Sedimentology 10, 255-272.

Ernst, W.G, Calvert, S.E. (1969) An experimental study of the recrystallization of porcelanite and its bearing on the origin of some bedded cherts. American Journal of Science 267-A, 114-133.

Eugster, H.P. (1969) Inorganic bedded cherts from the Magadi area, Kenya. Contributions to Mineralogy and Petrology 22, 1-31.

Mizutani, S. (1970) Silica minerals in the early stage of diagenesis. Sedimentology 15, 419-436.

Buurman, P., van der Plas, L. (1971) The genesis of Belgian and Dutch flints and cherts. Geologie en Mijnbouw 50, 9-28.

Calvert, S.E. (1971) Composition and origin of North Atlantic deep sea cherts. Contributions to Mineralogy and Petrology 33, 273-288.

Thurston, D.R. (1972) Studies on bedded cherts. Contributions to Mineralogy and Petrology 36, 329-334.

Lancelot, Y. (1973) Chert and Silica Diagenesis in Sediments from the Central Pacific. Deep Sea Drilling Project Reports and Publications 17, 377-405.

Meyers, W.J. (1977) Chertification in the Mississippian Lake Valley Formation, Sacramento Mountains, New Mexico. Sedimentology 24, 75-105.

Mizutani, S. (1977) Progressive ordering of cristobalitic silica in the early stage of diagenesis. Contributions to Mineralogy and Petrology, 61, 129-140.

Hein, J.R., Vallier, T.L, Allan, M.A. (1981) Chert Petrology and Geochemistry, Mid-Pacific Mountains and Hess Rise, Deep Sea Drilling Project Leg 62. Deep Sea Drilling Project Reports and Publications 62, 711-748.

Pisciotto, K.A. (1981) Diagenetic trends in the siliceous facies of the Monterey Shale in the Santa Maria region, California. Sedimentology 28, 547-571.

Riech, V. (1981) Siliceous sediments from the Nauru basin: Diagenetic alteration of biogenic opal and authigenesis of silica and silicates. Deep Sea Drilling Project Reports and Publications 61, 523-531.

Levitan, M.A., Strizhov, V.P., Schevtchenko, A.Y. (1983) Cherts from the Rio Grande Rise Sediments, Deep Sea Drilling Project Leg 72, Hole 516F. Deep Sea Drilling Project Reports and Publications 72, 443-447.

Laschet, C. (1984) On the origin of cherts. Facies 10, 257-290.

Hesse, R. (1989) Silica Diagenesis: Origin of Inorganic and Replacement Cherts. Earth-Science Reviews 26, 253-284.

Bustillo, M.A., Ruiz-Ortiz, P.A. (1987) Chert occurrences in carbonate turbidites: examples from the Upper Jurassic of the Betic Mountains (southern Spain). Sedimentology 34, 611-621.

Maliva, R.G., Knoll, A.H., Siever, R. (1989) Secular change in chert distribution: A reflection of evolving biological participation in the silica cycle. Palaios 4, 519-532.

Maliva, R.G., Siever, R. (1989) Chertification histories of some Late Mesozoic and Middle Paleozoic platform carbonates. Sedimentology 36, 907-926.

Compton, J.S (1991) Origin and diagenesis of clay minerals in the Monterey Formation, Santa Maria Basin are, California. Clay and Clay Minerals 39, 449-466.

Knauth, L.P. (1994) Petrogenesis of chert. In: Reviews in Mineralogy, Vol.29, Silica - Physical behavior, geochemistry and materials applications, Mineralogical Society of America.

Cady, S.L., Wenk, H.-R., Downing, K.H. (1996) HRTEM of microcrystalline opal in chert and porcelanite from the Monterey Formation, California. American Mineralogist 81, 1380-1395.

Sugitani, K., Yamamoto, K., Adachi, M., Kawabe, I., Sugisaki, R. (1998) Archean cherts derived from chemical, biogenic and clastic sedimentation in a shallow restricted basin: examples from the Gorge Creek Group in the Pilbara Block. Sedimentology 45, 1045-1062.

Hopkinson, L., Roberts, S., Herrington, R., Wilkinson, J. (1999) The nature of crystalline silica from the TAG submarine hydrothermal mound, 26°N Mid Atlantic Ridge. Contributions to Mineralogy and Petrology 137, 342-350.

Rosière, C.A., Chemale Jr., F. (2000) Brazilian iron formations and their geological setting. Revista Brasiliera de Geosciências 30, 274-278.

Gutzmer, J., Pack, A., Lüders, V., Wilkinson, J.J., Beukes, N.J., van Niekerk, H.S. (2001) Formation of jasper and andradite during low-temperature hydrothemal seafloor metamorphism, Ongeluk Formation, South Africa. Contributions to Mineralogy and Petrology 142, 27-42.

Grenne, T., Slack, J.F. (2003) Bedded jaspers of the Ordovician Løkken ophiolite, Norway: seafloor deposition and diagenetic maturation of hydrothermal plume-derived silica-iron gels. Mineralium Deposita 38, 625-639.

Maliva, R.G., Knoll, A.H, Simonson, B.M. (2005) Secular change in the Precambrian silica cycle: Insights from chert petrology. Geological Society of America Bulletin 117, 835-845.

Fischer, W.W., Knoll, A.H. (2008) An iron shuttle for deepwater silica in Late Archean and early Paleoproterozoic iron formation. Geological Society of America Bulletin 121, 222-235.

Madsen, H.B., Stemmerik, L. (2010) Diagenesis of flint and procellanite in the Maastrichtian chalk at Stevns Klint, Denmark. Journal of Sedimentary Research 80, 578-588.


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