clay

(klā)

1. 1. A fine-grained, firm earthy material that is plastic when wet and hardens when heated, consisting primarily of hydrated silicates of aluminum and widely used in making bricks, tiles, and pottery.
   2. A hardening or nonhardening material having a consistency similar to clay and used for modeling.
2. Geology. A sedimentary material with grains smaller than 0.002 millimeters in diameter.
3. Moist sticky earth; mud.
4. The human body as opposed to the spirit.

[Middle English clei, from Old English clæg.]

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The finest-grain particles in a sediment, soil, or rock. Clay is finer than silt, characterized by a grain size of less than approximately 4 micrometers. However, the term clay can also refer to a rock or a deposit containing a large component of clay-size material. Thus clay can be composed of any inorganic materials, such as clay minerals, allophane, quartz, feldspar, zeolites, and iron hydroxides, that possess a sufficiently fine grain size. Most clays, however, are composed primarily of clay minerals. See also Clay minerals; Feldspar; Quartz; Zeolite.

Although the composition of clays can vary, clays can share several properties that result from their fine particle size. These properties include plasticity when wet, the ability to form colloidal suspensions when dispersed in water, and the tendency to flocculate (clump together) and settle out in saline water. See also Colloid.

Clays, together with organic matter, water, and air, are one of the four main components of soil. Clays can form directly in a soil by precipitation from solution (neoformed clays); they can form from the partial alteration of clays already present in the soil (transformed clays); or they can be inherited from the underlying bedrock or from sediments transported into the soil by wind, water, or ice (inherited clays). See also Soil.

The type of clays neoformed in a soil depends on the composition of the soil solution, which in turn is a function of climate, drainage, original rock type, vegetation, and time. Generally, neoformed clays that have undergone intense leaching, such as soils formed under wet, tropical climates, are composed of the least soluble elements, such as ferric iron, aluminum, and silicon. These soils contain clays such as gibbsite, kaolinite, goethite, and amorphous oxides and hydroxides of aluminum and iron. Clays formed in soils that are found in dry climates or in soils that are poorly drained can contain more soluble elements, such as sodium, potassium, calcium, and magnesium, in addition to the least soluble elements. These soils contain clays such as smectite, chlorite, and illite, and generally are more fertile than those formed under intense leaching conditions. See also Chlorite; Goethite; Illite; Kaolinite.

Examples of clays formed by the transformation of other clays in a soil include soil chlorite and soil vermiculite, the first formed by the precipitation of aluminum hydroxide in smectite interlayers, and the second formed by the leaching of interlayer potassium from illite. Examples of inherited clays in a soil are illite and chlorite-containing soils formed on shales composed of these minerals. See also Shale.

Clays also occur abundantly in sediments and sedimentary rocks. For example, clays are a major component of many marine sediments. These clays generally are inherited from adjacent continents, and are carried to the ocean by rivers and wind, although some clays (such as smectite and glauconite) are neoformed abundantly in the ocean. Hydrothermal clays can form abundantly where rock has been in contact with hot water or steam. Illite and chlorite, for example, form during the deep burial of sediments, and smectite and chlorite form by the reaction of hot, circulating waters at ocean ridges. See also Marine sediments; Sedimentary rocks.

Various clays possess special properties which make them important industrially. For example, bentonite, a smectite formed primarily from the alteration of volcanic ash, swells; is readily dispersible in water; and possesses strong absorptive powers, including a high cation exchange capacity. These properties lead to uses in drilling muds, as catalysts and ion exchangers, as fillers and absorbents in food and cosmetics, and as binders for taxonite and fertilizers. Other important uses for clays include the manufacture of brick, ceramics, molding sands, decolorizers, detergents and soaps, medicines, adhesives, liners for ponds and landfills, lightweight aggregate, desiccants, molecular sieves, pigments, greases, paints, plasticizing agents, emulsifying, suspending, and stabilizing agents, and many other products. See also Bentonite; Catalysis; Clay, commercial; Ion exchange; Refractory.

geology The smallest particle size, typically less than 4μm or 0.002 in, but dependent on the scheme employed.

A dried mineral clay under the names of sikor, mithi, pakhuri, and khatta, is sometimes used in Asia as a treatment for indigestion and a nutritional supplement, but can be toxic since it contains varying amounts of arsenic and lead.

In addition to the idiom beginning with clay, also see feet of clay.

1. A geological deposit, such as Oxford Clay.

2. In a soil, mineral particles less than 0.002 mm in size. When dry, clay is hard; when wet it swells and becomes pliable and sticky. Clay colloids are finely divided clays dispersed in water. These particles have a negative surface charge which attracts positively charged ions. These minute particles are among the most reactive constituents of a soil. Clay micelles are individual clay particles, platey in form, with a diameter of less than 2 μ m, having a negative charge and therefore being able to attract cations within a soil.

A fine-grained, cohesive, natural earthy material; plastic when sufficiently wet; rigid when dried; vitrified when heated in a kiln to a sufficiently high temperature; used in making brick, as wall infilling, and as daub in wattle-and-daub.

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• Materials, Formations, and Substances - clay: soil composed of fine particles of hydrous aluminum silicates, plastic when wet, and hard when exposed to high temperature and/or pressure
• Soils and Soil Management - clay: firm, fine-grained soil, plastic when wet
• Ceramics and Glassmaking - clay: potter’s clay
• Dead Bodies - clay: Slang. dead and buried body

For other uses, see Clay (disambiguation).

The Gay Head cliffs in Martha's Vineyard consist almost entirely of clay.

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter.^[1] Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.

Contents 1 Formation 2 Definition 3 Grouping 4 Historical and modern uses 4.1 Medical and agricultural uses 4.2 Clay as a building material 5 See also 6 Footnotes 7 References 8 External links

Formation

Deforestation for clay extraction in Rio de Janeiro city - Brazil. The picture is of Morro da Covanca - Jacarepaguá.

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 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 depositional environments such as large lakes and marine basins.

Primary clays, also known as kaolins, are located at the site of formation. Secondary clay deposits have been moved by erosion and water from their primary location.^[2]

Definition

electron microscope photograph of smectite clay - magnification 23,500

Clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, 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. Geologists and soil scientists usually consider the separation to occur at a particle size of 2 µm (clays being finer than silts), sedimentologists often use 4-5 μm, and colloid chemists use 1 μm.^[1] 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.

Quaternary clay in Estonia.

Grouping

Depending on the academic source, there are three or four main groups of clays: kaolinite, montmorillonite-smectite, illite, and chlorite. Chlorites are not always considered a clay, sometimes being classified as a separate group within the phyllosilicates. 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 deposit is common in former glacial lakes. 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.^[2]

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 landslides.

Historical and modern uses

Clay layers in a construction site. Dry clay is normally much more stable than sand with regard to excavations.

Clays exhibit plasticity when mixed with water in certain proportions. When dry, clay becomes firm and when 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 minerals 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]} 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 called a stylus.

Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, dishware, and even musical instruments 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 filtering. Clay is also often used in the manufacture of pipes for smoking tobacco. Until the late 20th century bentonite clay was widely used as a mold binder in the manufacture of sand castings.

Clay, being relatively impermeable to water, is also used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage (lining the landfill, preferably in combination with geotextiles).^[3]

Recent^[when?] studies have investigated clay's absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification.

Medical and agricultural uses

A traditional use of 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 parrots (and later, humans) in South America originally used it.^[4] 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, 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 has a collection of quotations related to: Clay

Clay minerals Bentonite Ceramic Clay (industrial plasticine) Clay animation Clay court Clay pit Geophagy (eating of soils, including eating of clay) Expansive clay

London Clay Modelling clay Paperclay Particle size Plasticine Pottery Vertisol Graham Cairns-Smith, proposed the 'clay theory' of abiogenesis

Footnotes

1. ^ ^{a b} Guggenheim & Martin 1995, pp. 255–256
2. ^ ^{a b} Environmental Characteristics of Clays and Clay Mineral Deposits - USGS
3. ^ Koçkar, Mustafa K.; Akgün, Haluk; Aktürk, Özgür, Preliminary evaluation of a compacted bentonite / sand mixture as a landfill liner material (Abstract). Department of Geological Engineering, Middle East Technical University, Ankara, Turkey
4. ^ Evolutionary biology: Dirty eating for healthy living by Jared M. Diamond

References

• Guggenheim, Stephen; Martin, R. T. (1995), "Definition of clay and clay mineral: Journal report of the AIPEA nomenclature and CMS nomenclature committees", Clays and Clay Minerals 43 (2): 255–256, doi:10.1346/CCMN.1995.0430213, http://www.clays.org/journal/archive/volume%2043/43-2-255.pdf 
• 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

Look up clay in Wiktionary, the free dictionary.

Wikimedia Commons has media related to: Clay

• Building the Phyllosilicates University of New Hampshire
• The Clay Minerals Group of the Mineralogical Society
• Clay Whistles
• Information about clays used in the UK pottery industry
• The Clay Minerals Society
• Plasticity of clay
• Organic Matter in Clays

v d e Topics in geotechnical engineering Soils Clay · Silt · Sand · Gravel · Peat · Loam · Loess Soil properties Hydraulic conductivity · Water content · Void ratio · Bulk density · Thixotropy · Reynolds' dilatancy · Angle of repose · Cohesion · Porosity · Permeability · Specific storage Soil mechanics Effective stress · Pore water pressure · Shear strength · Overburden pressure · Consolidation · Soil compaction · Soil classification · Shear wave · Lateral earth pressure Geotechnical investigation Cone penetration test · Standard penetration test · Exploration geophysics · Monitoring well · Borehole Laboratory tests Atterberg limits · California bearing ratio · Direct shear test · Hydrometer · Proctor compaction test · R-value · Sieve analysis · Triaxial shear test · Hydraulic conductivity tests · Water content tests Field tests Crosshole sonic logging · Nuclear Densometer Test Foundations Bearing capacity · Shallow foundation · Deep foundation · Dynamic load testing · Pile integrity test · Wave equation analysis · Statnamic load test Retaining walls Mechanically stabilized earth · Soil nailing · Tieback · Gabion · Slurry wall Slope stability Mass wasting · Landslide · Slope stability analysis Earthquakes Soil liquefaction · Response spectrum · Seismic hazard · Ground-structure interaction Geosynthetics Geotextile · Geomembranes · Geosynthetic clay liner · Cellular confinement Instrumentation for Stability Monitoring Deformation monitoring · Automated Deformation Monitoring

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Dansk (Danish)
n. - ler
v. tr. - dække/blande med ler, filtrere gennem ler

idioms:

• clay feet    løvefødder på møbler
• clay pigeon    lerdue

Nederlands (Dutch)
klei, stenen pijp, karakter

Français (French)
n. - argile, glaise, terre glaise
v. tr. - mélanger ou couvrir d'argile, filtrer de l'argile

idioms:

• clay feet    pied d'argile
• clay pigeon    pigeon d'argile

Deutsch (German)
n. - Ton, Lehm
v. - mit Ton überziehen, mit Ton vermischen

idioms:

• clay feet    Schwachstelle
• clay pigeon    Tontaube

Ελληνική (Greek)
n. - άργιλος, πηλός
v. - ανακατεύω ή μαλάσσω πηλό, επιστρώνω ή επιχρίω με πηλό

idioms:

• clay feet    πήλινα πόδια
• clay pigeon    δίσκος σκοποβολής

Italiano (Italian)
argilla

idioms:

• clay feet    piedi di argilla
• clay pigeon    piattello

Português (Portuguese)
n. - argila (f), o corpo (m) humano (fig.)
v. - cobrir de barro ou argila

idioms:

• clay feet    fraquezas
• clay pigeon    disco (m) de argila arremessado como alvo, alvo (m) fácil (gír.)

Русский (Russian)
глина

idioms:

• clay feet    на глиняных ногах
• clay pigeon    тарелочка для стрельбы

Español (Spanish)
n. - arcilla, barro
v. tr. - mezclar o cubrir con barro o arcilla, filtrar a través de la arcilla

idioms:

• clay feet    pies de barro
• clay pigeon    plato (de tiro al platillo)

Svenska (Swedish)
n. - lera, stoft och aska (om människan), kritpipa (vard.), jord
v. - blanda m lera, täcka m lera

中文（简体）(Chinese (Simplified))
泥土, 粘土, 肉体

idioms:

• clay feet    泥足
• clay pigeon    泥制飞靶, 易被捉弄的人

中文（繁體）(Chinese (Traditional))
n. - 泥土, 粘土, 肉體

idioms:

• clay feet    泥足
• clay pigeon    泥製飛靶, 易被捉弄的人

한국어 (Korean)
n. - 점토, 진흙, 인간
v. tr. - 진흙을 섞다, 진흙으로 덮다, 진흙으로 여과 시키다

日本語 (Japanese)
n. - 粘土

idioms:

• clay feet    もろい土台
• clay pigeon    クレー

العربيه (Arabic)
‏(الاسم) طين, طمى (فعل) يطين, يمزج مع الطين, يغطي بالطين‏

עברית (Hebrew)
n. - ‮חומר, טיט‬

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