The standard free energies of formation of a number of zeolites were estimated using the polymer model developed previously for smectites by Sposito. The estimates made with the polymer model were on average within 19kJmol - 1 (0.28%) of the experimental values for zeolites; this compares with the values estimated by the methods of LaIglesia and Aznar and of Chermak and Rimstidt which differed from the experimental values on average by approximately 27kJmol - 1 (0.40%) and 32kJmol - 1 (0.47%) respectively. The values predicted by the polymer model for dehydrated zeolites were within 28kJmol - 1 (0.3%) of the experimental values, whereas the other two methods generate estimates of free energies of formation values that differed on average by 89kJmol - 1 (1.28%) and 107kJmol - 1 (1.59%) from the experimental values. These comparisons indicate that the polymer model, formulated specifically for a class of silicate minerals such as zeolites, always typically provides a better estimate of the standard free energy values than general models for all silicate minerals which contain a number of ad hoc assumptions. Better estimates provided by the polymer model can be attributed to the principle that the free energy changes associated with the formation of condensation polymers, such as zeolites, are related principally with the free energy changes associated with the relative change in coordination of exchangeable cations as they transfer from reactant hydroxide sites to exchangeable sites.