clay

Clay is a natural earth material composed mainly of fine-grained minerals known as clay minerals, along with small amounts of other minerals, organic matter, and water. By convention, individual clay particles are smaller than 2 micrometers in diameter, and soils with a high clay fraction are typically plastic when wet.

Most common clay minerals are layered aluminosilicates. They consist of sheets of tetrahedrally coordinated silicon or aluminum linked to octahedrally coordinated aluminum or magnesium, forming 1:1 (kaolinite group) and 2:1 (illite, smectite) structures. 2:1 clays can swell with water and generally have higher surface area and cation-exchange capacity.

Clay forms by weathering and chemical alteration of silicate minerals in the presence of water, becoming concentrated in soils and sedimentary rocks as fine-grained layers. It is widespread in shale, mudstone, and clay-rich deposits around the world.

Key properties include high surface area, plasticity when moist, and low permeability. Water content governs plasticity; clays exhibit cation-exchange capacity and can swell or shrink in response to hydration, with smectites showing the most swelling and kaolinite remaining relatively non-swelling.

Uses of clay include ceramics such as pottery, bricks, and tiles; cement and binders; drilling fluids; paper fillers; cosmetics; and various industrial absorbents and sealants. The particular properties of a clay determine its suitability for a given application.

Commercial processing typically involves mining, washing, drying, grinding, and refining to produce powders, slips, or suspensions tailored for firing temperatures and desired textures.