o types (i), (ii) and (iii).Zeolites (Aluminosilicates of Alkali Metals and/or of Alkaline Earth Metals)These may be described by the following general formula M.sub.x/n[(AlO.sub.2).sub.x(SiO.sub.2).sub.y].wH.sub.2O, where n is the charge on the cation M; M is an element of the first or second main group, such as Li, Na, K, Mg, Ca, Sr or Ba; y:x isa number from 0.8 to 15, preferably from 0.8 to 1.