Physicochemical characterization of the natural solid-phase Gordes clinoptilolite and of the Na+-, K+, Ca2+- and Mg2+-modified forms of the mineral (as obtained through ion-exchange) by batch methods, X-ray diffractometry (XRD), X-ray fluorescence (XRF), infrared spectroscopy (IR) and scanning electron microscopy (SEM) is described. It was found that the Na+- and Ca2+-forms exhibit high ion-exchange rates relative to the Mg2+- and K+-forms. In addition, the high rate of ion selectivity towards Na+ and K+ ions, together with lower rates for Mg2+ and Ca2+ ions, indicate that the rate of ion selectivity is negatively correlated with the ionic potential of the ions. Such ion-exchange and ion selectivity result in a decrease in pore size and an increase in the surface area of the modified clinoptilolite relative to the natural form; this may possibly be related to the entrance of the ions into the mineral structure. It was concluded that clinoptilolite modified with exchangeable ions from aqueous solutions at two different normalities exhibits features which differ from those of natural clinoptilolite. Thus, modification of clinoptilolite by different cationic forms from aqueous solutions at different normalities might prove suitable for applications in other fields of study.