Zeolites are crystalline nanoporous hydrated aluminosilicates in which linked Si, O, & Al form a three-dimensional framework Structure. The linkages create surface pores of uniform (2 to 10?) diameter enclosing regular internal cavities and channels with the discrete size and shape depending on the zeolite species. The cavities contain loosely bound metal cations that can engage in ion exchange as well as water molecules that can be reversibly driven off. In theory the possibilities for framework topologies are infinite, although in practice around 40 are known in nature and more than 150 synthetic zeolites have been manufactured. For the record, the empirical formula for a zeolite is M+2.M++) Al2O3.gSiO2.zH2O where M+ is usually Na or K & M++ is Mg. Ca. or Fe. Rarely Li, Sr, or Ba may substitute for M+ or M++.