Argiles

Argiles, in geology and soil science, refers to fine-grained natural earth materials that are composed predominantly of clay minerals. The particles are typically smaller than 4 micrometers in diameter, giving argiles their characteristic plasticity and high surface area. The principal clay minerals include kaolinite, illite, montmorillonite (a smectite), and chlorite; quartz and feldspar may be present as accessory minerals.

Argiles form by chemical weathering of silicate rocks, or by alteration of existing clays, and they accumulate in low-energy settings such as lakes, river floodplains, lagoons, or deep-sea basins. When deposited and lithified, rocks with high clay content are called argillaceous rocks, notably shales and mudstones, sometimes referred to as argillites in older literature.

Key properties of argiles derive from their plate-like structure and high surface area. They exhibit plasticity and cohesion when wet, shrink-swell behavior on moisture changes, and a high cation exchange capacity that influences nutrient retention and pollutant adsorption. Their behavior is highly sensitive to water content and pH.

In industry and environment, clays are used in ceramics (pots, bricks, tiles), cement and construction additives, paper production, and drilling fluids. They play a central role in soils, affecting fertility, structure, porosity, and erosion risk. Classification of argiles typically follows mineralogy (kaolinite-dominant, illite-dominant, smectite-rich) and origin (primary versus secondary clays).