Above is the schematic figure showing the structure of the
crystal lattice of Montmorillonite.
is made up of two outer silica sheets composed of SiO4
-tetrahedrons and a central sheets comprised of Aluminium
cations surrounded in octahedral from by oxide anions of
By introducing trivalent
Aluminium and iron ions into the central sheet, the interlayer
space is provided by the presence of cations which are capable
of exchange and can be easily replaced by the others of
stronger binding affinity. Crude clays consist of calcium ions
as well and such Bentonites are known as calcium Bentonite.