View source for Clay

{{Short description|Fine grained natural soil}}
{{Other uses}}
{{Use dmy dates|date=May 2020}}
{{Use British English|date=March 2021}}

'''Clay''' is a type of fine-grained natural [[soil]]  material containing [[clay mineral]]s{{sfn|Olive|Chleborad|Frahme|Shlocker|1989}} (hydrous aluminium phyllosilicates, e.g. [[kaolinite]], {{chem2|[[Al]]2[[Si]]2[[O]]5([[hydroxide|OH]])4}}). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impurities, such as a reddish or brownish colour from small amounts of [[iron oxide]].{{sfn|Klein|Hurlbut|1993|pp=512–514}}{{sfn|Nesse|2000|pp=252–257}}

Clays develop [[plasticity (physics)|plasticity]] when wet but can be hardened through [[Pottery#Firing|firing]].{{sfn|Guggenheim|Martin|1995|pp=255–256}}{{sfn|Science Learning Hub|2010}}{{sfn|Breuer|2012}} Clay is the longest-known [[ceramic]] material. Prehistoric humans discovered the useful properties of clay and used it for making [[pottery]]. Some of the earliest pottery shards have been [[radiocarbon dating|dated]] to around 14,000&nbsp;BCE,{{sfn|Scarre|2005|p=238}} and [[Clay tablet|clay tablets]] were the first known writing medium.{{sfn|Ebert|2011|p=64}} Clay is used in many modern industrial processes, such as [[paper]] making, [[cement]] production, and chemical [[filtration|filtering]]. Between one-half and two-thirds of the world's population live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure.{{citation needed|date=June 2025}} In agriculture, clay content is a major factor in determining land [[arable land|arability]]. Clay soils are generally less suitable for crops due to poor natural drainage; however, clay soils are more fertile, due to higher [[cation-exchange capacity]].<ref name="v874">{{cite book | title=Lockhart and Wiseman' s Crop Husbandry Including Grassland | chapter=Soil health and management | publisher=Elsevier | date=2023 | isbn=978-0-323-85702-4 | doi=10.1016/b978-0-323-85702-4.00023-6 | pages=49–79}}</ref><ref name="x742">{{cite web | title=Cation Exchange Capacity and Base Saturation | website=UGA Cooperative Extension | date=2014-02-26 | url=https://extension.uga.edu/publications/detail.html?number=C1040&title=cation-exchange-capacity-and-base-saturation | access-date=2025-01-08}}</ref>

Clay is a very common substance. [[Shale]], formed largely from clay, is the most common sedimentary rock.{{sfn|Boggs|2006|p=140}} Although many naturally occurring deposits include both silts and clay, 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. Mixtures of [[sand]], silt and less than 40% clay are called [[loam]]. Soils high in ''swelling clays'' ([[expansive clay]]), which are clay minerals that readily expand in volume when they absorb water, are a major challenge in [[civil engineering]].{{sfn|Olive|Chleborad|Frahme|Shlocker|1989}}

== Properties ==
[[File:Clay magnified.jpg|thumb|A 23,500 times magnified electron micrograph of [[smectite]] clay]]
The defining mechanical property of clay is its plasticity when wet and its ability to harden when dried or fired. Clays show a broad range of water content within which they are highly plastic, from a minimum water content (called the [[Atterberg limits|plastic limit]]) where the clay is just moist enough to mould, to a maximum water content (called the liquid limit) where the moulded clay is just dry enough to hold its shape.{{sfn|Moreno-Maroto|Alonso-Azcárate|2018}} The plastic limit of kaolinite clay ranges from about 36% to 40% and its liquid limit ranges from about 58% to 72%.{{sfn|White|1949}} High-quality clay is also tough, as measured by the amount of mechanical work required to roll a sample of clay flat. Its toughness reflects a high degree of internal cohesion.{{sfn|Moreno-Maroto|Alonso-Azcárate|2018}}

Clay has a high content of clay minerals that give it its plasticity. Clay minerals are [[hydrate|hydrous]] [[aluminium]] [[Silicate minerals#Phyllosilicates|phyllosilicate minerals]], composed of aluminium and silicon ions bonded into tiny, thin plates by interconnecting oxygen and [[hydroxide]] ions. These plates are tough but flexible, and in moist clay, they adhere to each other. The resulting aggregates give clay the cohesion that makes it plastic.{{sfn|Bergaya|Theng|Lagaly|2006|pp=1-18}} In [[kaolinite]] clay, the bonding between plates is provided by a film of water molecules that [[hydrogen bond]] the plates together. The bonds are weak enough to allow the plates to slip past each other when the clay is being moulded, but strong enough to hold the plates in place and allow the moulded clay to retain its shape after it is moulded. When the clay is dried, most of the water molecules are removed, and the plates form direct hydrogen bonds with each other, making the dried clay rigid but still fragile. If the clay is moistened again, it will once more become plastic. When the clay is fired to the [[earthenware]] stage, a [[dehydration reaction]] removes additional water from the clay, causing clay plates to irreversibly adhere to each other via stronger [[covalent bonding]], which strengthens the material. The clay mineral kaolinite is transformed into a non-clay material, [[metakaolin]], which remains rigid and hard if moistened again. Further firing through the [[stoneware]] and [[porcelain]] stages further recrystallizes the metakaolin into yet stronger minerals such as [[mullite]].{{sfn|Breuer|2012}}

The tiny size and plate form of clay particles gives clay minerals a high surface area. In some clay minerals, the plates carry a negative electrical charge that is balanced by a surrounding layer of positive ions ([[cation]]s), such as sodium, potassium, or calcium. If the clay is mixed with a solution containing other cations, these can swap places with the cations in the layer around the clay particles, which gives clays a high capacity for [[ion exchange]].{{sfn|Bergaya|Theng|Lagaly|2006|pp=1-18}} The chemistry of clay minerals, including their capacity to retain nutrient cations such as potassium and ammonium, is important to soil fertility.{{sfn|Hodges|2010}}

Clay is a common component of [[sedimentary rock]]. Shale is formed largely from clay and is the most common of sedimentary rocks.{{sfn|Boggs|2006|p=140}} However, most clay deposits are impure. Many naturally occurring deposits include both silts and clay. 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. There is, however, some overlap in particle size and other physical properties. 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.{{sfn|Guggenheim|Martin|1995|pp=255–256}} Clay-size particles and clay minerals are not the same, despite a degree of overlap in their respective definitions. [[Geotechnical engineering|Geotechnical engineers]] distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' [[Atterberg limits]]. [[International Organization for Standardization|ISO]] 14688 grades clay particles as being smaller than 2 μm and silt particles as being larger. Mixtures of sand, silt and less than 40% clay are called loam.

Some clay minerals (such as [[smectite]]) are described as swelling clay minerals, because they have a great capacity to take up water, and they increase greatly in volume when they do so. When dried, they shrink back to their original volume. This produces distinctive textures, such as [[mudcrack]]s or "popcorn" texture, in clay deposits. Soils containing swelling clay minerals (such as [[bentonite]]) pose a considerable challenge for civil engineering, because swelling clay can break foundations of buildings and ruin road beds.{{sfn|Olive|Chleborad|Frahme|Shlocker|1989}}

=== Agriculture ===
Clay is generally considered undesirable for agriculture, although some amount of clay is a necessary component of good soil. Compared to other soils, clay soils are less suitable for crops due to their tendency to retain water, and require artificial [[drainage]] and [[tillage]] to make suitable for planting. However, clay soils are often more fertile and can hold onto nutrients better due to their higher [[cation-exchange capacity]], allowing more land to remain in production rather than being left [[fallow]]. As clay tends to retain nutrients for longer before leaching them, this also means plants may require more fertilizer in clay soils.<ref name="v874"/><ref name="x742"/>

== Formation ==
[[File: Italian and African-American Clay Miners in Mine Shaft.jpg|thumb|Italian and African-American clay miners in mine shaft, 1910]]

Clay minerals most commonly form by prolonged chemical [[weathering]] of silicate-bearing rocks. They can also form locally from [[hydrothermal]] activity.{{sfn|Foley|1999}} Chemical weathering takes place largely by acid hydrolysis due to low concentrations of [[carbonic acid]], dissolved in rainwater or released by plant roots. The acid breaks bonds between aluminium and oxygen, releasing other metal ions and silica (as a gel of [[orthosilicic acid]]).){{sfn|Leeder|2011|pp=5-11}}

The clay minerals formed depend on the composition of the source rock and the climate. Acid weathering of [[feldspar]]-rich rock, such as [[granite]], in warm climates tends to produce kaolin. Weathering of the same kind of rock under alkaline conditions produces [[illite]]. [[Smectite]] forms by weathering of [[igneous rock]] under alkaline conditions, while [[gibbsite]] forms by intense weathering of other clay minerals.{{sfn|Leeder|2011|pp=10-11}}

There are two types of clay deposits: primary and secondary. Primary clays form as residual deposits in soil and remain at the site of formation. Secondary clays are clays that have been transported from their original location by water erosion and [[Deposition (geology)|deposited]] in a new [[sedimentary]] deposit.{{sfn|Murray|2002}} Secondary clay deposits are typically associated with very low energy [[Depositional environment|depositional environments]] such as large lakes and marine basins.{{sfn|Foley|1999}}

== Varieties ==
The main groups of clays include [[kaolin]]ite, [[montmorillonite]]-[[smectite]], and [[illite]]. [[Chlorite group|Chlorite]], [[vermiculite]],{{sfn|Nesse|2000|p=253}} [[talc]], and [[pyrophyllite]]{{sfn|Klein|Hurlbut|1993|pp=514-515}} are sometimes also classified as clay minerals. There are approximately 30 different types of "pure" clays in these categories, but most "natural" clay deposits are mixtures of these different types, along with other weathered minerals.{{sfn|Klein|Hurlbut|1993|p=512}} Clay minerals in clays are most easily identified using [[Clay mineral X-ray diffraction|X-ray diffraction]] rather than chemical or physical tests.{{sfn|Nesse|2000|p=256}}

[[Varve]] (or ''varved clay'') is clay with visible annual layers that are formed by seasonal deposition of those layers and are marked by differences in [[erosion]] and organic content. This type of deposit is common in former [[glacial lake]]s. When fine sediments are delivered into the calm waters of these glacial lake basins away from the shoreline, they settle to the lake bed. The resulting seasonal layering is preserved in an even distribution of clay sediment banding.{{sfn|Foley|1999}}

[[Quick clay]] is a unique type of [[marine clay]] indigenous to the glaciated terrains of Norway, North America, Northern Ireland, and Sweden.{{sfn|Rankka|Andersson-Sköld|Hultén|Larsson|2004}} It is a highly sensitive clay, prone to [[Soil liquefaction|liquefaction]], and has been involved in several deadly [[landslide]]s.{{sfn|Natural Resources Canada|2005}}

== Uses ==
[[File: Clay In A Construction Site.jpg|thumb|Clay layers in a construction site in [[Auckland]], New Zealand. Dry clay is normally much more stable than sand in excavations.]]
[[File:Diósgyőr - 2015.02.07 (145).JPG|thumb|upright|left|A 14th-century [[Stopper (plug)|bottle stopper]] made of [[fire clay|fired clay]]]]
[[Modelling clay]] is used in art and handicraft for [[sculpting]]. Clays are used for making [[pottery]], both utilitarian and decorative, and construction products, such as bricks, walls, and floor tiles. 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. Some of the earliest pottery shards recovered are from central [[Honshu]], [[Japan]]. They are associated with the [[Jōmon period|Jōmon]] culture, and recovered deposits have been [[radiocarbon dating|dated]] to around 14,000&nbsp;BCE.{{sfn|Scarre|2005|p=238}} Cooking pots, art objects, dishware, [[smoking pipe (tobacco)|smoking pipes]], and even [[musical instrument]]s such as the [[ocarina]] can all be shaped from clay before being fired. 

Ancient peoples in [[Mesopotamia]] adopted clay tablets as the first known writing medium.{{sfn|Ebert|2011|p=64}} Clay was chosen due to the local material being easy to work with and widely available.<ref>{{Cite web |title=British Library |url=https://www.bl.uk/history-of-writing/articles/a-brief-history-of-writing-materials-and-technologies#:~:text=The%20earliest%20material%20used%20to,drawn%20into%20with%20a%20stylus. |access-date=2023-05-09 |website=www.bl.uk |archive-date=12 September 2022 |archive-url=https://web.archive.org/web/20220912141816/https://www.bl.uk/history-of-writing/articles/a-brief-history-of-writing-materials-and-technologies#:~:text=The%20earliest%20material%20used%20to,drawn%20into%20with%20a%20stylus. |url-status=dead }}</ref> Scribes wrote on the tablets by inscribing them with a script known as [[cuneiform]], using a blunt [[reed (plant)|reed]] called a [[stylus]], which effectively produced the wedge shaped markings of their writing. After being written on, clay tablets could be reworked into fresh tablets and reused if needed, or fired to make them permanent records. Nowadays, clay is added as a filler to [[graphite]], in pencil lead, to change the hardness and blackness of the [[pencil]]. Purpose-made clay balls were used as [[sling (weapon)#Ammunition|sling ammunition]].{{sfn|Forouzan|Glover|Williams|Deocampo|2012}} Clay is used in many industrial processes, such as [[paper]] making, [[cement]] production, and chemical [[filter (chemistry)|filtering]].{{sfn|Nesse|2000|p=257}} [[Bentonite]] clay is widely used as a mold binder in the manufacture of [[sand casting]]s.{{sfn|Boylu|2011}}{{sfn|Eisenhour|Brown|2009}}
{{external media
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| topic  = as a type of relaxation
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[[File:Bain d'argile à Gogotinkpon au Bénin 01.jpg|thumb|Clay bath near [[lake Ahémé]] in [[Benin]]]]

=== Materials ===

Clay is a common filler used in polymer [[nanocomposites]]. It can reduce the cost of the composite, as well as impart modified behavior: increased [[stiffness]], decreased [[Permeation|permeability]], decreased [[electrical conductivity]], etc.<ref>{{cite journal |last1=Kotal |first1=M. |last2=Bhowmick |first2=A. K. |title=Polymer nanocomposites from modified clays: Recent advances and challenges |journal=Progress in Polymer Science |date=2015 |volume=51 |pages=127–187 |doi=10.1016/j.progpolymsci.2015.10.001}}</ref>

=== Medicine ===
Traditional uses of [[medicinal clay|clay as medicine]] go back to prehistoric times. An example is [[Armenian bole]], which is used to soothe an upset stomach. Some animals such as parrots and pigs ingest clay for similar reasons.{{sfn|Diamond|1999}} [[Kaolin|Kaolin clay]] and [[attapulgite]] have been used as anti-diarrheal medicines.{{sfn|Dadu|Hu|Cleeland|Busaidy|2015}}

=== Construction ===
[[File:WMEE-exp2019-(113).jpg|thumb|left|A clay building in [[South Estonia]]]]
Clay as the defining ingredient of loam is one of the oldest [[building material]]s on [[Earth]], among other ancient, naturally occurring geologic materials such as stone and organic materials like wood.{{sfn|Grim|2016}} {{cn span|date=December 2020|Between one-half and two-thirds of the world's population, in both traditional societies as well as developed countries, still live or work in buildings made with clay, often baked into brick, as an essential part of their load-bearing structure.}} Also a primary ingredient in many [[natural building]] techniques, clay is used to create [[adobe]], [[cob (material)|cob]], [[cordwood]], and structures and building elements such as [[wattle and daub]], clay plaster, clay render case, clay floors and clay [[paints]] and [[ceramic building material]]. Clay was used as a [[mortar (masonry)|mortar]] in brick [[chimneys]] and stone walls where protected from water.

Clay, relatively [[permeability (fluid)|impermeable]] to water, is also used where [[Puddling (civil engineering)|natural seals]] are needed, such as in pond linings, the cores of [[dam]]s, or as a barrier in [[landfill]]s against toxic seepage (lining the landfill, preferably in combination with [[geotextile]]s).{{sfn|Koçkar|Akgün|Aktürk|2005}} Studies in the early 21st century have investigated clay's [[sorption|absorption]] capacities in various applications, such as the removal of [[heavy metals]] from waste water and air purification.{{sfn|García-Sanchez|Alvarez-Ayuso|Rodriguez-Martin|2002}}{{sfn|Churchman|Gates|Theng|Yuan|2006}}

== See also ==
{{div col}}
* {{annotated link|Argillaceous minerals}}
* {{annotated link|Industrial plasticine}}
* {{annotated link|Clay animation}}
* {{annotated link|Clay chemistry}}
* {{annotated link|Clay court}}
* {{annotated link|Clay panel}}
* {{annotated link|Clay pit}}
* {{annotated link|Geophagia}}
* {{annotated link|Graham Cairns-Smith}}
* {{annotated link|London Clay}}
* {{annotated link|Modelling clay}}
* {{annotated link|Paper clay}}
* {{annotated link|Particle size}}
* {{annotated link|Plasticine}}
* {{annotated link|Vertisol}}
* {{annotated link|Clay–water interaction}}
{{div col end}}

== Notes ==
{{reflist}}

== References ==
* [http://www.minsocam.org/msa/collectors_corner/arc/nomenclaturecl1.htm Clay mineral nomenclature] ''American Mineralogist''.
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* {{cite book |last1=Boggs |first1=Sam |title=Principles of sedimentology and stratigraphy |date=2006 |publisher=Pearson Prentice Hall |location=Upper Saddle River, N.J. |isbn=0131547283 |edition=4th}}
* {{cite journal |last1=Boylu |first1=Feridun |title=Optimization of foundry sand characteristics of soda-activated calcium bentonite |journal=Applied Clay Science |date=1 April 2011 |volume=52 |issue=1 |pages=104–108 |doi=10.1016/j.clay.2011.02.005|bibcode=2011ApCS...52..104B }}
* {{cite journal |last1=Breuer |first1=Stephen |title=The chemistry of pottery |journal=Education in Chemistry |date=July 2012 |pages=17–20 |url=https://www.qvevriproject.org/Files/2012.07.00_RSC_Breuer_ChemistryOfPottery.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.qvevriproject.org/Files/2012.07.00_RSC_Breuer_ChemistryOfPottery.pdf |archive-date=2022-10-09 |url-status=live |access-date=8 December 2020}}
* {{cite journal|title = Chapter 11.1 Clays and Clay Minerals for Pollution Control|publisher = Elsevier|journal = Developments in Clay Science|date = 2006|pages = 625–675|volume = 1|series = Handbook of Clay Science|first1 = G. J.|last1 = Churchman|first2 = W. P.|last2 = Gates|first3 = B. K. G.|last3 = Theng|first4 = G.|last4 = Yuan|editor-first = Benny K. G. Theng and Gerhard Lagaly|editor-last = Faïza Bergaya|doi=10.1016/S1572-4352(05)01020-2|isbn = 9780080441832}}
* {{cite journal |last1=Dadu |first1=Ramona |last2=Hu |first2=Mimi I. |last3=Cleeland |first3=Charles |last4=Busaidy |first4=Naifa L. |last5=Habra |first5=Mouhammed |last6=Waguespack |first6=Steven G. |last7=Sherman |first7=Steven I. |last8=Ying |first8=Anita |last9=Fox |first9=Patricia |last10=Cabanillas |first10=Maria E. |title=Efficacy of the Natural Clay, Calcium Aluminosilicate Anti-Diarrheal, in Reducing Medullary Thyroid Cancer–Related Diarrhea and Its Effects on Quality of Life: A Pilot Study |journal=Thyroid |date=October 2015 |volume=25 |issue=10 |pages=1085–1090 |doi=10.1089/thy.2015.0166|pmid=26200040 |pmc=4589264 }}
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* {{Cite book|url=https://books.google.com/books?id=HNHyiDm3__kC&q=Clay+tablets+were+the+first+known+writing+medium&pg=PA64|title=The New Media Invasion: Digital Technologies and the World They Unmake|last=Ebert|first=John David|date=31 August 2011|publisher=McFarland|isbn=9780786488186|url-status=live|archive-url=https://web.archive.org/web/20171224225732/https://books.google.com/books?id=HNHyiDm3__kC&pg=PA64&dq=Clay+tablets+were+the+first+known+writing+medium&hl=en&sa=X&ved=0ahUKEwj-mMuxz5XVAhXixVQKHUpZCPQQ6AEIKTAB#v=onepage&q=Clay%20tablets%20were%20the%20first%20known%20writing%20medium&f=false|archive-date=24 December 2017}}
* Ehlers, Ernest G. and Blatt, Harvey (1982). 'Petrology, Igneous, Sedimentary, and Metamorphic' [[San Francisco]]: W.H. Freeman and Company.  {{ISBN|0-7167-1279-2}}.
* {{cite journal |last1=Eisenhour |first1=D. D. |last2=Brown |first2=R. K. |title=Bentonite and Its Impact on Modern Life |journal=Elements |date=1 April 2009 |volume=5 |issue=2 |pages=83–88 |doi=10.2113/gselements.5.2.83|bibcode=2009Eleme...5...83E }}
* {{cite web|url=https://pubs.usgs.gov/info/clays/|last1=Foley |first1=Nora K.|date=September 1999|title=Environmental Characteristics of Clays and Clay Mineral Deposits|work=usgs.gov|url-status=live|archive-url=https://web.archive.org/web/20081208055734/http://pubs.usgs.gov/info/clays/|archive-date=8 December 2008}}
* {{cite journal |last1=Forouzan |first1=Firoozeh |last2=Glover |first2=Jeffrey B. |last3=Williams |first3=Frank |last4=Deocampo |first4=Daniel |title=Portable XRF analysis of zoomorphic figurines, "tokens," and sling bullets from Chogha Gavaneh, Iran |journal=Journal of Archaeological Science |date=1 December 2012 |volume=39 |issue=12 |pages=3534–3541 |doi=10.1016/j.jas.2012.04.010|bibcode=2012JArSc..39.3534F }}
* {{cite journal|title = Sorption of As(V) by some oxyhydroxides and clay minerals. Application to its immobilization in two polluted mining soils|journal = Clay Minerals|date = 1 March 2002|pages = 187–194|volume = 37|issue = 1|doi = 10.1180/0009855023710027|first1 = A.|last1 = García-Sanchez|first2 = E.|last2 = Alvarez-Ayuso|first3 = F.|last3 = Rodriguez-Martin|df = dmy-all|bibcode = 2002ClMin..37..187G|s2cid = 101864343}}
* {{cite web|last1=Grim|first1=Ralph|year=2016|title=Clay mineral|url=https://www.britannica.com/science/clay-mineral|website=[[Encyclopædia Britannica]]|access-date=10 January 2016|url-status=live|archive-url=https://web.archive.org/web/20151209182021/https://www.britannica.com/science/clay-mineral|archive-date=9 December 2015}}
* {{Citation| last1 =Guggenheim| first1 =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| doi =10.1346/CCMN.1995.0430213| issue =2|bibcode = 1995CCM....43..255G | s2cid =129312753| doi-access = }}
* 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.
* {{cite web |last1=Hodges |first1=S.C. |year=2010 |title=Soil fertility basics |publisher=Soil Science Extension, North Carolina State University |url=http://www2.mans.edu.eg/projects/heepf/ilppp/cources/12/pdf%20course/38/Nutrient%20Management%20for%20CCA.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www2.mans.edu.eg/projects/heepf/ilppp/cources/12/pdf%20course/38/Nutrient%20Management%20for%20CCA.pdf |archive-date=2022-10-09 |url-status=live |access-date=8 December 2020}}
* {{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut | first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st}}
* {{cite web |last1=Koçkar |first1=Mustafa K. |last2=Akgün |first2=Haluk |last3=Aktürk |first3=Özgür  |date=November 2005|url=http://www2.widener.edu/~sxw0004/abstract34.html |title=Preliminary evaluation of a compacted bentonite / sand mixture as a landfill liner material (Abstract)] |archive-url=https://web.archive.org/web/20081204075553/http://www2.widener.edu/~sxw0004/abstract34.html |archive-date=4 December 2008 |website=Department of Geological Engineering, [[Middle East Technical University]], [[Ankara]], [[Turkey]]}}
* {{cite book |last1=Leeder |first1=M. R. |title=Sedimentology and sedimentary basins : from turbulence to tectonics |date=2011 |publisher=Wiley-Blackwell |location=Chichester, West Sussex, UK |isbn=978-1-40517783-2 |edition=2nd}}
* {{cite journal |last1=Moreno-Maroto |first1=José Manuel |last2=Alonso-Azcárate |first2=Jacinto |title=What is clay? A new definition of "clay" based on plasticity and its impact on the most widespread soil classification systems |journal=Applied Clay Science |date=September 2018 |volume=161 |pages=57–63 |doi=10.1016/j.clay.2018.04.011|bibcode=2018ApCS..161...57M |s2cid=102760108 }}
* {{cite journal |last1=Murray |first1=H. |year=2002 |title=Industrial clays case study |journal=Mining, Minerals and Sustainable Development |volume=64 |pages=1–9 |url=http://whitemudresources.com/public/Hayn%20Murray%20Clays%20Case%20Study.pdf |access-date=8 December 2020 |archive-date=20 April 2021 |archive-url=https://web.archive.org/web/20210420140406/http://whitemudresources.com/public/Hayn%20Murray%20Clays%20Case%20Study.pdf |url-status=dead }}
* {{cite web | url=http://geoscape.nrcan.gc.ca/ottawa/landslides_e.php | title=Landslides | publisher=[[Natural Resources Canada]] | work=Geoscape Ottawa-Gatineau | date=7 March 2005 | access-date=2016-07-21 | archive-url=https://web.archive.org/web/20051024191116/http://geoscape.nrcan.gc.ca/ottawa/landslides_e.php | archive-date=24 October 2005 | url-status=dead |ref={{harvid|Natural Resources Canada|2005}}}}
* {{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916}}
* {{cite journal |last1=Olive |first1=W.W. |last2=Chleborad |first2=A.F. |last3=Frahme |first3=C.W. |last4=Shlocker |first4=Julius |last5=Schneider |first5=R.R. |last6=Schuster |first6=R.L. |year=1989 |url=https://ngmdb.usgs.gov/Prodesc/proddesc_10014.htm |access-date=8 December 2020 |title=Swelling Clays Map of the Conterminous United States |journal=U.S. Geological Survey Miscellaneous Investigations Series Map |volume=I-1940|page=5 |doi=10.3133/i1940 |bibcode=1989usgs.rept....5O |url-access=subscription }}
* {{cite web | url=http://www.swedgeo.se/publikationer/Rapporter/pdf/SGI-R65.pdf | title=Quick clay in Sweden | publisher=Swedish Geotechnical Institute | work=Report No. 65 | date=2004 | access-date=20 April 2005 | last1=Rankka | first1=Karin | last2=Andersson-Sköld | first2=Yvonne | last3=Hultén | first3=Carina | last4=Larsson | first4=Rolf | last5=Leroux | first5=Virginie | last6=Dahlin | first6=Torleif | archive-url=https://web.archive.org/web/20050404064431/http://www.swedgeo.se/publikationer/Rapporter/pdf/SGI-R65.pdf | archive-date=4 April 2005 | url-status=dead}}
* {{cite book |last1=Scarre |first1=C. |year=2005 |title=The Human Past |publisher=Thames and Hudson |location=London |isbn=0500290636}}
* {{cite web|title=What is clay|url=http://sciencelearn.org.nz/Contexts/Ceramics/Science-Ideas-and-Concepts/What-is-clay|website=Science Learning Hub|publisher=[[University of Waikato]]|access-date=10 January 2016|url-status=live|archive-url=https://web.archive.org/web/20160103182308/http://sciencelearn.org.nz/Contexts/Ceramics/Science-Ideas-and-Concepts/What-is-clay|archive-date=3 January 2016 |ref={{harvid|Science Learning Hub|2010}} }}
* {{cite journal |last1=White |first1=W.A. |year=1949 |title=Atterberg plastic limits of clay minerals |journal=American Mineralogist |volume=34 |issue=7–8 |pages=508–512 |url=http://www.minsocam.org/ammin/AM34/AM34_508.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.minsocam.org/ammin/AM34/AM34_508.pdf |archive-date=2022-10-09 |url-status=live |access-date=7 December 2020}}

== External links ==
{{Wiktionary}}
{{Commons category|Clay}}
{{EB1911 poster|Clay}}
{{Wikiquote}}
* [http://www.minersoc.org/pages/groups/cmg/cmg.html The Clay Minerals Group of the Mineralogical Society] {{Webarchive|url=https://web.archive.org/web/20170926234633/http://www.minersoc.org/pages/groups/cmg/cmg.html |date=26 September 2017 }}
* [https://web.archive.org/web/20090217000619/http://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://digitalfire.com/4sight/education/organic_matter_in_clays_detailed_overview_325.html Organic Matter in Clays]
* [[usgs.gov]] (Mineral Commodity Summaries 2025): [https://pubs.usgs.gov/periodicals/mcs2025/mcs2025.pdf#page=50 Clays] 

{{soil type}}
{{Geotechnical engineering|state=collapsed}}
{{Authority control}}

[[Category:Clay| ]]
[[Category:Types of soil]]
[[Category:Sculpture materials]]
[[Category:Natural materials]]
[[Category:Sedimentology]]
[[Category:Sediments]]
[[Category:Soil-based building materials]]