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clay

  (klā) pronunciation
n.
    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.]

clayey clay'ey (klā'ē) or clay'ish adj.
 
 
Sci-Tech Encyclopedia: Clay

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.

 
Food and Nutrition: clay

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.

 
Idioms: clay

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

 
Measures and Units: clay

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

 
Geography Dictionary: 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.

 
Britannica Concise Encyclopedia: clay

Soil particles with diameters less than 0.005 mm; also a material composed essentially of clay particles (see clay mineral). In soils, clays provide the environment for almost all plant growth. The use of clay in pottery making predates recorded human history. As building materials, clay bricks (baked and as adobe) have been used in construction since earliest times. Kaolin, or china clay, is required for the finer grades of ceramic materials; used for paper coating and filler, it gives the paper a gloss, permitting high-quality reproduction, and increases paper opacity. Clay materials have many uses in engineering; earth dams are made impermeable to water by a core of clay, and water loss in canals may be reduced by lining the bottom with clay (called puddling). The essential raw materials of portland cement include clays.

For more information on clay, visit Britannica.com.

 
Architecture: clay

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.

 
Archaeology Dictionary: clay

[Ma]

1. Extremely fine particles, less than 0.002mm across forming constituent components of natural and anthropogenic sediments and deposits.

2. The plastic raw material from which pottery, daub, bricks, and other forms of terracotta are made comprising mainly clay-sized particles of the principal clay minerals kaolinite, illite, and montmorillonite. Potting clay is a relatively abundant and widespread resource, although the quality and characteristics of different outcrops vary greatly, the best being highly sought-after.

3. A general term describing the texture and feel of a sediment: soft, sticky, and plastic when wet, hard when dry.
 
Columbia Encyclopedia: clay,
common name for a number of fine-grained, earthy materials that become plastic when wet. Chemically, clays are hydrous aluminum silicates, ordinarily containing impurities, e.g., potassium, sodium, calcium, magnesium, or iron, in small amounts.

Properties and Classification

Properties of the clays include plasticity, shrinkage under firing and under air drying, fineness of grain, color after firing, hardness, cohesion, and capacity of the surface to take decoration. On the basis of such qualities clays are variously divided into classes or groups; products are generally made from mixtures of clays and other substances. The purest clays are the china clays and kaolins. “Ball clay” is a name for a group of plastic, refractory (high-temperature) clays used with other clays to improve their plasticity and to increase their strength. Bentonites are clays composed of very fine particles derived usually from volcanic ash. They are composed chiefly of the hydrous magnesium-calcium-aluminum silicate called montmorillonite. See also fuller's earth.

Individual clay particles are always smaller than 0.004 mm. Clays often form colloidal suspensions when immersed in water, but the clay particles flocculate (clump) and settle quickly in saline water. Clays are easily molded into a form that they retain when dry, and they become hard and lose their plasticity when subjected to heat.

Formation

Clays are divided into two classes: residual clay, found in the place of origin, and transported clay, also known as sedimentary clay, removed from the place of origin by an agent of erosion and deposited in a new and possibly distant position. Residual clays are most commonly formed by surface weathering, which gives rise to clay in three ways—by the chemical decomposition of rocks, such as granite, containing silica and alumina; by the solution of rocks, such as limestone, containing clayey impurities, which, being insoluble, are deposited as clay; and by the disintegration and solution of shale. One of the commonest processes of clay formation is the chemical decomposition of feldspar.

Clay consists of a sheet of interconnected silicates combined with a second sheetlike grouping of metallic atoms, oxygen, and hydroxyl, forming a two-layer mineral such as kaolinite. Sometimes the latter sheetlike structure is found sandwiched between two silica sheets, forming a three-layer mineral such as vermiculite. In the lithification process, compacted clay layers can be transformed into shale. Under the intense heat and pressure that may develop in the layers, the shale can be metamorphosed into slate.

Uses

From prehistoric times, clay has been indispensable in architecture, in industry, and in agriculture. As a building material, it is used in the form of brick, either sun-dried (adobe) or fired. Clays are also of great industrial importance, e.g., in the manufacture of tile for wall and floor coverings, of porcelain, china, and earthenware, and of pipe for drainage and sewage. Highly absorbent, bentonite is much used in foundry work for facing the molds and preparing the molding sands for casting metals. The less absorbent bentonites are used chiefly in the oil industry, e.g., as filtering and deodorizing agents in the refining of petroleum and, mixed with other materials, as drilling muds to protect the cutting bit while drilling. Other uses are in the making of fillers, sizings, and dressings in construction, in clarifying water and wine, in purifying sewage, and in the paper, ceramics, plastics, and rubber industries.

Clay as a Soil

Clay is one of the three principal types of soil, the other two being sand and loam. A certain amount of clay is a desirable constituent of soil, since it binds other kinds of particles together and makes the whole retentive of water. Excessively clayey soils, however, are exceedingly difficult to cultivate. Their stiffness presents resistance to implements, impedes the growth of the plants, and prevents free circulation of air around the roots. They are cold and sticky in wet weather, while in dry weather they bake hard and crack. Clods form very often in clayey soils. Clays can be improved by the addition of lime, chalk, or organic matter; sodium nitrate, however, intensifies the injurious effects. In spite of their disadvantages, the richness of clay soils makes them favorable to the growth of crops that have been started in other soil.

Bibliography

See R. E. Grim, Clay Mineralogy (2d ed. 1968); R. W. Grimshaw, The Chemistry and Physics of Clays and Allied Ceramic Materials (4th ed. 1971).

 
Word Tutor: clay
pronunciation

IN BRIEF: Mud that can be used to make ceramics, tiles or bricks.

pronunciation A vessel is formed from a lump of clay with care, however, it is the empty space within the vessel that makes it useful. — Lao Tzu, Source: Tao Te Ching

 
Wikipedia: clay
The Gay Head cliffs in Martha's Vineyard are made almost entirely of clay.
Enlarge
The Gay Head cliffs in Martha's Vineyard are made almost entirely of clay.

Clay is a naturally occurring material, composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried or fired. Clay deposits are mostly composed of clay minerals (phyllosilicate minerals), minerals which impart plasticity and harden when fired or dried, and variable amounts of water trapped in the mineral structure by polar attraction. Organic matter and materials which do not impart plasticity may also be a part of clay deposits.[1]

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, 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 lake and marine deposits.

Definition

Clays are distinguished from other fine-grained soils by various distinctions. Silts, which are fine-grained soils which 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 both silts and clays. 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, silts being coarser), 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.

Quaternary clay in Estonia.
Enlarge
Quaternary clay in Estonia.

Grouping

Depending upon 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 thirty 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.

Quick clay is a unique type of marine clay indigenous to the glaciated terrains of Norway, Canada 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 regards to excavations.
Enlarge
Clay layers in a construction site. Dry clay is normally much more stable than sand with regards 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 reactions occur which, amongst other changes, causes the clay to be converted into a ceramic material. It is because of these properties that clay is used for making pottery items, both practical and decorative. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware, stoneware and porcelain. Early humans discovered the useful properties of clay in prehistoric times, and one of the earliest artifacts ever uncovered is a drinking vessel made of sun-dried clay. Depending on the content of the soil, clay can appear in various colors, from a dull gray to a deep orange-red.

Clay was also used as the very first writing medium. Thousands of years BCE the cuneiform script was written in clay tablets with a blunt reed called a stylus.

Clays sintered in fire were the first form of ceramic, and remains one of the cheapest to produce and most widely used materials to this day. 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. Additionally, Clay is often used in the manufacture of pipes for smoking tobacco.

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).[2]

Recent studies have been carried out to investigate clay's adsorption capacities in various applications, such as the removal of heavy metals from waste water and air purification.

See also

Footnotes

  1. ^ a b Guggenheim & Martin 1995, pp. 255–256
  2. ^ Preliminary evaluation of a compacted bentonite / sand mixture as a landfill liner material (Abstract) - Koçkar, Mustafa K.; Akgün, Haluk; Aktürk, Özgür; Department of Geological Engineering, Middle East Technical University, Ankara, Turkey

References

  • Ehlers, Ernest G. and Blatt, Harvey (1982). 'Petrology, Igneous, Sedimentary, and Metamorphic' San Francisco: W.H. Freeman and Company. ISBN 0-7167-1279-2.

External links

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Translations: Translations for: Clay

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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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved.  Read more
Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.  Read more
Food and Nutrition. A Dictionary of Food and Nutrition. Copyright © 1995, 2003, 2005 by A. E. Bender and D. A. Bender. All rights reserved.  Read more
Idioms. The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Company. All rights reserved.  Read more
Measures and Units. A Dictionary of Weights, Measures, and Units. Copyright © Donald Fenna 2002, 2004. All rights reserved.  Read more
Geography Dictionary. A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved.  Read more
Architecture. McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc. All rights reserved.  Read more
Archaeology Dictionary. The Concise Oxford Dictionary of Archaeology. Copyright © 2002, 2003 by Oxford University Press. All rights reserved.  Read more
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