montmorillonite

Montmorillonite is a very soft phyllosilicate group of minerals that typically form as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite group, is a 2:1 clay, meaning that it has two tetrahedral sheets of silica sandwiching a central octahedral sheet of alumina. The particles are plate-shaped with an average diameter around 1 µm and a thickness of 9.6X10^-9 m. Members of this group include saponite.