1. n. [Geology]

[(1/2Ca,Na)0.7(Al,Mg,Fe)4(Si,Al)8O20(OH)47nH2O)]

A group of clay minerals that includes montmorillonite. This type of mineral tends to swell when exposed to water. Bentonite includes minerals of the smectite group.

See related terms: bentonite,  clay,  hectorite,  mineral,  montmorillonite