The water molecules can also be reversibly driven off in most zeolites. Chabazite and clinoptilolite are the two out of the 48 minerals in the zeolite group which have commercial applications. These deposits of high purity zeolite minerals occur in Cenozoic age tuffaceous sediments principally in the Western United States. Chabazite and Clinoptilolite which formed over a long period of time are the end product of the chemical reaction between volcanic ash consisting of glass shards and alkaline water. Because of their high silica to alumina ratios ranging from 2 to 1 for chabazite to 5 to 1 for clinoptilolite, these minerals are stable and less likely to dealuminate in acidic solutions than are synthetic zeolites.
Zeolites are crystalline hydrated aluminosilicates, of the alkali and alkaline earth metals.
Their crystalline framework is arranged in an interconnecting lattice structure. The arrangement of these elements in a zeolite crystal, creates a porous framework silicate structure with interconnecting channels that range in size from 2.5 to 4.3 angstroms, depending on the zeolite mineral. The adsorption functions identified above are accomplished when gas molecules of different sizes are allowed to pass through the channels, and depending upon the size of the channel are separated as to size, in a process known as molecular sieving. Each zeolite mineral has a distinct ion exchange selectivity and capacity. This process occurs when water molecules can pass through the channels and pores allowing cations present in the solution to be exchanged for cations in the structure.