1. Thermoanalytical TG, DTG, and DTA curves have been obtained, first for the natural clinoptilolites from the Nor Kokhb and Khekordzula beds in Armenia and Georgia, and then for modified forms of these minerals prepared by ion-exchange methods. 2. The DTA and DTG curves for these minerals show minima at 170, 270, 470, 610, and 800°C, the indication being that several forms of water are bound in the clinoptilolite canals. The K+, Na+, and Ca2+ ion aquo complexes decompose at 170, 270, and 470°C, respectively. 3. Chemical analysis, and ion exchange and thermoanalytical studies, suggest that the Armenian clinoptilolites contain considerable quantities of calcite which breaks down at ∼800°C.