Montmorillonit is a very soft layered silicate mineral. When they precipitate from an aqueous solution, they form microscopic crystals called clays. This is a 2:1 clay, which means it has two tetrahedral silicon chips in the middle and one octahedral alumina chip. These particles are plate-shaped, with an average diameter of about 1 μm and a thickness of 0.96 nm; under an electron microscope at around 25,000x magnification, it is necessary to see individual clay particles.
As a 2:1 layered silicate mineral, its octahedral charge is greater than fifty percent. Its cation exchange capacity is due to the in-plane substitution of Al by Mg isomorphs in alumina. In this case, the substitution of a low valence cation gives the nearby oxygen atom a net negative charge and can attract the cation. On the other hand, there is a type of product with a tetrahedral charge greater than fifty percent, which originates from the isomorphic substitution of aluminum in the silica flakes.