montmorilloniet

Montmorillonite is a clay mineral of the smectite group and a layered aluminosilicate. Its structure features two silica tetrahedral sheets around an alumina-magnesium octahedral sheet (a 2:1 layer). Interlayer cations such as Na+ or Ca2+ and water molecules swell the mineral, giving high plasticity and significant swelling in water. The composition is typically represented as (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2·nH2O and it has a high cation-exchange capacity and large surface area.

Montmorillonite forms by the weathering or alteration of volcanic ash, especially in bentonite deposits. The mineral was first described in Montmorillon, a town in west-central France, and the name is retained for many bentonite clays found around the world.

Deposits are widespread, with major commercial bentonite beds in the United States (Wyoming), France, Greece, China, and India. Montmorillonite is commonly associated with other smectites and clays formed in volcanic or sedimentary environments.

Uses of montmorillonite reflect its swelling, adsorptive and rheological properties. It is employed in drilling fluids to control viscosity and filtration, and as a barrier material in landfill liners and sealing systems. It serves as a binder in foundries, a component of cement and grouts, and an adsorbent for oils and pollutants. In cosmetics and pharmaceuticals, it is used as a thickener and stabilizer due to its high surface area and swelling behavior. Safety and handling considerations focus on dust generation and inertness, with standard industrial hygiene practices advised.