Term: Clay

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**Properties of Clay:**
– Clay exhibits plasticity when wet and hardens when dried or fired.
– The plastic limit of kaolinite clay ranges from 36% to 40%.
– High-quality clay is tough due to internal cohesion.
– Clay minerals are hydrous aluminium phyllosilicate minerals.
– Clay particles have high surface area and ion exchange capacity.
– High plasticity and cohesion when wet, shrinks and cracks when dried, expands when wet.
– Cation exchange capacity for nutrient retention.
– Varied colors depending on mineral content.
– Ability to retain water and nutrients in soil.

**Formation and Varieties of Clay:**
– Clay minerals form through prolonged chemical weathering of silicate-bearing rocks.
– Acid hydrolysis from carbonic acid in rainwater contributes to chemical weathering.
– Composition of source rock and climate influence the type of clay minerals formed.
– Clay deposits can be primary (residual) or secondary (transported by water erosion).
– Secondary clay deposits are linked to low energy depositional environments.
– Main clay groups include kaolinite, montmorillonite-smectite, and illite.
– Chlorite, vermiculite, talc, and pyrophyllite are sometimes classified as clay minerals.

**Uses of Clay:**
– Clays used in art, pottery, construction, and manufacturing of bricks, walls, and floor tiles.
– Clay used in making cooking pots, art objects, dishware, smoking pipes, and musical instruments.
– Clay tablets adopted in Mesopotamia as the first known writing medium.
– Industrial uses of clay in paper making, cement production, and chemical filtering.
– Bentonite clay widely used as a mold binder in sand castings.
– Soil conditioning and fertility improvement.
– Absorbent in cat litter, oil spill cleanup, and facial masks.
– Component in drilling fluids for oil and gas wells.
– Used in pottery making, bricks, and tiles.
– Important in pharmaceuticals for antidiarrheal treatments.

**Medicinal and Construction Applications of Clay:**
– Traditional use of clay as medicine dates back to prehistoric times.
– Kaolin clay and attapulgite used as anti-diarrheal medicines.
– Armenian bole used to soothe upset stomachs.
– Animals like parrots and pigs ingest clay for medicinal purposes.
– Clay used in mass bathing for relaxation.
– Clay, a primary ingredient in loam, is one of the oldest building materials.
– Between one-half and two-thirds of the world’s population live or work in clay buildings.
– Clay used in natural building techniques like adobe, cob, cordwood, and wattle and daub.
– Impermeable clay used in pond linings, dam cores, and landfills.
– Clay’s absorption capacities studied for applications like heavy metal removal and air purification.

**Geological and Scientific Significance of Clay:**
– Indicator of past environments and climates.
– Role in sedimentary rock formation.
– Influence on landslides and slope stability.
– Presence in marine, lacustrine, and terrestrial environments.
– Used in geotechnical engineering for soil stabilization.
– Research on clay mineralogy and petrology.
– Impact of clays on environmental processes.
– Analysis of clay minerals in archaeological artifacts.
– Sorption capacity of clays for pollutant immobilization.
– Definition and classification of clays by scientific committees.

Clay (Wikipedia)

Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, Al2Si2O5(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.

Gay Head Cliffs in Martha's Vineyard consist almost entirely of clay.
A quaternary clay in Estonia

Clays develop plasticity when wet but can be hardened through firing. 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 dated to around 14,000 BCE, and clay tablets were the first known writing medium. Clay is used in many modern industrial processes, such as paper making, cement production, and chemical 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.

Clay is a very common substance. Shale, formed largely from clay, is the most common sedimentary rock. 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. 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.

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