1. A PROCESS OF SEPARATING MICROQUANTITIES OF CESIUM VALUES FROM AQUEOUS SOLUTIONS CONTAINING WITH SAID CESIUM VALUES OTHER IONS IN MACROQUANTITIES, CONSISTING IN HEATING CLINOPTILOTILE AT ABOUT 400*C. FOR AT LEAST TWO HOURS, COOLING THE CLINOPTIOLITE TO ROOM TEMPERATURE, CONTACTING THE CLINOPTILITILE WITH SAID AQUEOUS SOLUTION TO BE TREATED, WHEREBY CESIUM IS PREFERENTIALLY TAKEN UP BY THE CLINOPTILOTILE, AND SEPARATING THE SOLUTION CONTAINING SAID OTHER IONS FROM THE CESIUM-CONTAINING CLINOPTILOLITE.