Soil material that contains clays minerals is known as clays. A molecular layer of water surrounds the clays particles, resulting in flexibility when the clays are wet but hard, brittle, and non-plastic when dried or fired. Various colours can come from impurities, such as reddish or brownish hues from iron oxide in natural clays minerals.
The first ceramic material discovered was clay. Prehistoric people found clays to have valuable characteristics, and it was put to use in the production of pottery. Chemical filtration and paper manufacturing are only a few modern-day applications for clays.
Clays’ mechanical properties are defined by their capacity to soften when wet and solidify when dry or heated. When the clays are just moist enough to mould, it has reached their “plasticity limit,” and when the clays reach their “liquid limit,” it has reached the point when it is just dry enough to keep their shape. Kaolinite clays have a plastic limit of around 36% to 40% and a liquid limit of about 58% to 72%. The amount of mechanical effort required to roll a sample of clays flat is a good indicator of the quality of the clays. A high level of internal cohesiveness is seen in its hardness.
Chemical weathering of silicate-bearing rocks is the most prevalent method for producing clays minerals. Hydrothermal activity can potentially lead to the formation of these structures.
Acid hydrolysis dominates chemical weathering due to rainwater’s low content of carbonic acid or plant roots’ release of carbonic acid.
They break aluminium-oxygen bonds with orthosilicic acid, resulting in different metals and silica releases.
Clay minerals are created according to the kind of rock and the environment. In warm regions, acid weathering of feldspar-rich rock such as granite creates kaolin.
Illite is a byproduct of alkaline weathering of the same type of rock. In alkaline settings, smectite originates from the weathering of igneous rock, while gibbsite forms from the weathering of clays minerals.
Primary and secondary clays deposits are available. Residual deposits of primary clays form in soil and remain there permanently. Secondary clays are clays that have been eroded by water erosion. Depositional settings such as vast lakes and ocean basins are common locations for secondary clays deposits.
Clays have been used for medicinal purposes since prehistoric times. Armenian boles are a common remedy for a churning stomach. Parrots and pigs ingest clays. Anti-diarrheal drugs include kaolin clays.
In addition to stone and organic elements like wood, clay is one of the most ancient construction materials since it is the defining constituent of loam. More than a half to two-thirds of the world’s population still lives or works in structures composed of clays, frequently baked into brick, as an integral element of its load-bearing construction. Many natural construction systems rely on clays, such as adobe, cob and cordwood. Clays are also used to produce wattle and daub, clays plaster, render casing, flooring, ceramic paints, and building material. Brick chimneys employed clays mortar, and stone walls were waterproofed with clays.
The engineering field makes extensive use of clays materials. Clays may be added to porous soil to make earth dams impervious to water, and they are also used to prevent water loss in canals. Limestone and impure clays are the primary basic materials used in Portland cement production. Clays have been employed as water softeners after acid treatment because they extract calcium and magnesium from the solution and replace the sodium in the solution with calcium and magnesium. In rotary drilling, clays are used as drilling mud, a mixture of chemical additives and weighing components, including clays.