Bentonite

Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite, (Na,Ca)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂·nH₂O. Two types exist: swelling bentonite which is also called sodium bentonite and non-swelling bentonite or calcium bentonite. It forms from volcanic ash that expands when wet and used to make slurry walls.

Bentonite is named after Benton Formation (a geological stratum, at one time Fort Benton Formation) in eastern Wyoming's Rock Creek area. Bentonite is mined in the southwestern US and in Greece. It can be used in cement, adhesives, ceramic fillers, cosmetics, and cat litter. Bentonite clay is also used in pyrotechnics to make end plugs and rocket nozzles. Most is used in the oil and gas well drilling industries.

Reference

• USGS Info