The main mineral component of bentonite is montmorillonite, with a content of 85-90%. Some properties of bentonite are also determined by montmorillonite.  

The structure of montmorillonite is a 2:1 type crystal structure composed of two silicon-oxygen tetrahedrons and a layer of aluminum-oxygen octahedron. There are some cations in the layered structure formed by the unit cell of montmorillonite. When the interlayer cation is Na+, it is called soudium bentonite; when the interlayer cation is Ca2+, it is called calcium bentonite; when the interlayer cation is an organic cation, it is called organic bentonite.