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Biography
other uses Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter.harvnb|Guggenheim|Martin|1995|pp=255–256 Geologic clay deposit (geology)|deposits are mostly composed of Silicate minerals#Phyllosilicates|phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.
Formation
Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents . These solvents, usually acidic, migrate through the weathering rock after Leaching (pedology)|leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits in soil, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy Sedimentary depositional environment|depositional environments such as large lakes and marine basins.
Primary clays, also known as Kaolinite|kaolins , are located at the site of formation. Secondary clay deposits have been moved by erosion and water from their primary location. http://pubs.usgs.gov/info/clays/ Environmental Characteristics of Clays and Clay Mineral Deposits - USGS
Definition
Clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silt s, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays, but there is some overlap in both particle size and other physical properties, and there are many naturally occurring deposits which include silts and also clay. The distinction between silt and clay varies by discipline. Geologist s and soil scientist s usually consider the separation to occur at a particle size of 2 Micrometre|µm (clays being finer than silts), sedimentologist s often use 4-5 µm, and colloid chemist s use 1 µm. Geotechnical engineering|Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg Limits . ISO 14688 grades clay particles as being smaller than 2 µm and silts larger.
Grouping
Depending on the academic source, there are three or four main groups of clays: kaolin ite, montmorillonite - smectite , illite , and chlorite group|chlorite . Chlorites are not always considered a clay, sometimes being classified as a separate group within the phyllosilicate s. There are approximately 30 different types of "pure" clays in these categories, but most "natural" clays are mixtures of these different types, along with other weathered minerals.
Varve (or varved clay ) is clay with visible annual layers, formed by seasonal differences in erosion and organic content. This type of deposition (geology)|deposit is common in former glacial lake s. When glacial lakes are formed there is very little movement of the water that makes the lake, and these eroded soils settle on the lake bed. This allows such an even distribution on the different layers of clay.
Quick clay is a unique type of marine clay indigenous to the glaciated terrains of Norway , Canada , Northern Ireland , and Sweden . It is a highly sensitive clay, prone to liquefaction , which has been involved in several deadly landslide s.
Historical and modern uses
Clays exhibit plasticity (physics)|plasticity when mixed with water in certain proportions. When dry, clay becomes firm and when pottery firing|fired in a kiln , permanent physical and chemical changes occur. These reactions, among other changes, cause the clay to be converted into a ceramic material. Because of these properties, clay is used for making pottery items, both utilitarian and decorative. Different types of clay, when used with different mineral s and firing conditions, are used to produce earthenware , stoneware , and porcelain . Prehistoric humans discovered the useful properties of clay, and one of the earliest artifacts ever uncovered is a drinking vessel made of sun-dried clay.citation needed|date=May 2008 Depending on the content of the soil, clay can appear in various colors, from a dull gray to a deep orange-red.
Clay tablets were used as the first known writing medium, inscribed with cuneiform script through the use of a blunt reed (plant)|reed called a stylus .
Clays sintering|sintered in fire were the first form of ceramic . Brick s, cooking pots, art objects, dishware , and even musical instrument s such as the ocarina can all be shaped from clay before being fired. Clay is also used in many industrial processes, such as paper making, cement production, and chemical filter (chemistry)|filter ing. Clay is also often used in the manufacture of smoking pipe (tobacco)|pipes for smoking tobacco . Until the late 20th century bentonite clay was widely used as a mold binder in the manufacture of sand casting s.
Clay, being relatively permeability (fluid)|impermeable to water, is also used where natural seals are needed, such as in the cores of dam s, or as a barrier in landfill s against toxic seepage (lining the landfill, preferably in combination with geotextile s).Koçkar, Mustafa K.; Akgün, Haluk; Aktürk, Özgür, http://www2.widener.edu/~sxw0004/abstract34.html Preliminary evaluation of a compacted bentonite / sand mixture as a landfill liner material (Abstract). Department of Geological Engineering, Middle East Technical University , Ankara , Turkey
Recentwhen|date=March 2011 studies have investigated clay's sorption|absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification.
Medical and agricultural uses
Recent research indicates that various animals visit clay lick s periodically to eat from them, apparently because either the clay contains one or more antidote s for the various poison s in plants and seeds the animals eat, or because the clay coats the animals' guts to protect them from those substances.cn|date=April 2012 A traditional use of medicinal clay|clay as medicine goes back to prehistoric times. An example is Armenian bole , which is used to soothe an upset stomach , similar to the way parrot s (and later, humans) in South America originally used it. http://cogweb.ucla.edu/Abstracts/Diamond_99.html Evolutionary biology: Dirty eating for healthy living by Jared M. Diamond Kaolin clay and attapulgite have been used as anti-diarrheal medicines.
Clay as a building material
Clay is one of the oldest building materials on Earth, among other ancient, naturally-occurring geologic materials such as stone and organic materials like wood. Between one-half and two-thirds of the world's population, in traditional societies as well as developed countries, still live or work in a building made with clay as an essential part of its load-bearing structure. Also a primary ingredient in many natural building techniques, clay is used to create adobe , cob (material)|cob , cordwood , and rammed earth structures and building elements such as wattle and daub , clay plaster, clay render case, clay floors and clay paints.
See also
wikiquote
Clay minerals
Bentonite
Ceramic
Clay (industrial plasticine)
Clay animation
Clay court
Clay pit
Geophagy (eating of soils, including eating of clay)
Graham Cairns-Smith , proposed the 'clay theory' of abiogenesis
Footnotes
reflist
References
Citation
| last =Guggenheim | first =Stephen | last2 =Martin | first2 =R. T. | title =Definition of clay and clay mineral: Journal report of the AIPEA nomenclature and CMS nomenclature committees | journal =Clays and Clay Minerals | volume =43 | pages =255–256 | year =1995 | url = http://www.clays.org/journal/archive/volume%2043/43-2-255.pdf | doi =10.1346/CCMN.1995.0430213 | issue =2
http://www.minsocam.org/msa/collectors_corner/arc/nomenclaturecl1.htm Clay mineral nomenclature American Mineralogist .
Ehlers, Ernest G. and Blatt, Harvey (1982). 'Petrology, Igneous, Sedimentary, and Metamorphic' San Francisco : W.H. Freeman and Company. ISBN 0-7167-1279-2.
Hillier S. (2003) Clay Mineralogy. pp 139–142 In: Middleton G.V., Church M.J., Coniglio M., Hardie L.A. and Longstaffe F.J.(Editors) Encyclopedia of sediments and sedimentary rocks. Kluwer Academic Publishers, Dordrecht.
External links
wiktionarycommons category|Clay
http://pubpages.unh.edu/~harter/crystal.htm Building the Phyllosilicates University of New Hampshire
http://www.minersoc.org/pages/groups/cmg/cmg.html The Clay Minerals Group of the Mineralogical Society
http://www.stoke.gov.uk/ccm/museums/museum/2006/gladstone-pottery-museum/information-sheets/clays-used-in-the-pottery-industry.en Information about clays used in the UK pottery industry
http://www.clays.org/ The Clay Minerals Society
http://www.ic.arizona.edu/ic/mse257/class_notes/plasticity.html Plasticity of clay
http://digitalfire.com/4sight/education/organic_matter_in_clays_detailed_overview_325.html Organic Matter in Clays
