Montmorillonite is a layered silicate belonging to the smectite group of phyllosilicate minerals. It is formed primarily by the alteration of extrusive volcanic rocks such as volcanic ash falls and ash fall tuffs. Commonly these minerals are products of geological weathering or hydrothermal alteration of silicate minerals and silica phases in these igneous rocks.
Montmorillonite occurs naturally as a sequence of stacked layers 1.0 to 1.5 nanometers thick. These layers are the fundamental building blocks of montmorillonite and are strongly two-dimensional. These layers are frequently described as “stacks of cards” or “layers of cards” to better describe their unique structure and form. As a result of its unique structure, montmorillonite possesses the ability to absorb large amounts of water and other liquids. The liquid is sorbed onto, or hydrates, the layers at the interlayer cation site, causing swelling. The result is a mineral that can absorb in 2-10 times its weight of liquid.
It is the absorption and swelling characteristics that makes montmorillonite so useful in industrial and commercial applications. Montmorillonite is used in cat litters, industrial oil absorbents, filtration media, animal feeds, soil amendments and agricultural applications.