Bentonite is a mineral composed essentially of the smectitic clay mineral called montmorillonite, formed from vitreous material of igneous origin that undergoes devitrification and chemical alteration.

It is normally classified as calcium bentonite and sodium bentonite. The latter shows greater interest for industrial applications, being used to provide plasticity, to act as a rheological modifier, suspending agent, ion adsorbent, particle binder, among other properties.