Clay

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

Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3 , MgO etc.) and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, and become hard, brittle and non–plastic upon drying or firing.[1][2][3] Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red.

Electron microscope photograph of smectite clay – magnification 23,500×

Although 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. 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 silt particles as being larger.

Mixtures of sand, silt and less than 40% clay are called loam. Loam makes good soil and is used as a building material.

Formation

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

Clay minerals typically form over long periods of time as a result of 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 through hydrothermal activity. 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 deposited in a new sedimentary deposit.[4] Clay deposits are typically associated with very low energy depositional environments such as large lakes and marine basins.

Other Languages
Afrikaans: Klei
Alemannisch: Ton (Bodenart)
አማርኛ: ሸክላ
العربية: صلصال
asturianu: Magre
Aymar aru: Llink'i laq'a
azərbaycanca: Gil
башҡортса: Балсыҡ
беларуская: Гліна
беларуская (тарашкевіца)‎: Гліна
български: Глина
bosanski: Glina
català: Argila
Чӑвашла: Тăм
čeština: Jíl
chiShona: Munyakwe
dansk: Ler
eesti: Savi
Ελληνικά: Άργιλος
español: Arcilla
Esperanto: Argilo
euskara: Buztin
فارسی: رس
français: Argile
Frysk: Klaai
Gaeilge: Cré
galego: Arxila
한국어: 점토
հայերեն: Կավ
हिन्दी: मृत्तिका
hrvatski: Glina (tlo)
Ido: Argilo
Bahasa Indonesia: Tanah liat
íslenska: Leir
italiano: Argilla
עברית: חרסית
Basa Jawa: Lempung
ქართული: თიხა
қазақша: Саз
Kiswahili: Udongo kinamo
Kreyòl ayisyen: Ajil (non)
Кыргызча: Чопо
Latina: Argilla
latviešu: Māls
lietuvių: Molis
Limburgs: Klei
lumbaart: Terra crea
magyar: Agyag
македонски: Глина
മലയാളം: കളിമണ്ണ്
Bahasa Melayu: Tanah liat
монгол: Шавар
Nederlands: Klei
日本語: 粘土
norsk: Leire
norsk nynorsk: Leire
occitan: Argila
polski: Glina
português: Argila
română: Argilă
Runa Simi: Ch'aqu
русский: Глина
संस्कृतम्: मृत्तिका
Scots: Cley
shqip: Deltina
sicilianu: Argilla
Simple English: Clay
SiSwati: Lubumba
slovenčina: Íl
slovenščina: Glina
Soomaaliga: Dhoobo
српски / srpski: Глина
srpskohrvatski / српскохрватски: Gline
suomi: Savi
svenska: Lera
Tagalog: Luwad
தமிழ்: களிமண்
татарча/tatarça: Балчык
Türkçe: Kil
українська: Глина
اردو: سفال
vèneto: Crèa
Tiếng Việt: Đất sét
West-Vlams: Klyte
粵語: 黏土
žemaitėška: Muolis
中文: 黏土