Natural Ion Exchangers:
Most of the natural ion exchange materials are crystalline aluminosilicates with cation exchange properties. The typical representative of this group of materials are zeolites which involve between others, the minerals such as analcite Na[SiAlO6]2. H2O, chabazite (CaNa)[SiAlO6]2.6H2O and naturalite Na2[Si2Al2O10].2H2O. All these minerals have a relatively open three dimensional framework with channels and interconnecting cavities in the aluminosilicate lattice. A zeolite lattice will consist of SiO4 and AlO4 tetrahedra. These have their oxygen atoms in common. Because aluminium is trivalent, the lattice carries a negative charge. The charge is balanced by alkali and alkaline earth cations which do not occupy fixed positions and are free to move in the lattice framework. Those ions behave as counter ions and could exchange along with other counter ions.
There are other aluminosilicates with loose layer structure having cation exchange properties. These materials carry their counterions in between the layer of the lattice. The typical mineral of this type is montmorillonite with the approximate composition Al2[Si4O10(OH)2].nH2O. Like minerals swell in one direction increasing the interlayer distance.