Bentonite is a soft, porous and easily shaped open rock, predominantly in colloidal silica structure, consisting of clay minerals with very small crystals (mainly montmorillonite) formed by the chemical weathering or degradation of volcanic ash, tuff and lava rich in aluminum and magnesium.

Scientifically, it was formed as a result of the devitrification of glassy igneous rocks, usually volcanic ash and molds, consisting of smectite group minerals as the main mineral with soft, plastic, porous, light-colored properties and containing colloidal silica.