Add to ORKGAbstract--Exchange isotherms for the pairs Na-K and Na-Ca were measured by use of 0.1 N solutions at 5 ~ 35 ~ and 70 ~ in phillipsite from Tecopa, California (3.63 A1/32 oxygen unit cell), and Oki Islands, Shi-mane Prefecture, Japan (6.31 A1/32 oxygen unit cell). All isotherms except hose for Na-Ca at 5 ~ were reversible. Free energy was evaluated for all reversible exchanges. The thermodynamic affinity sequences were K> Na> Ca in both phillipsites. The selectivity for K in competition with Na and that for Na com-peting with Ca became larger at the lower temperatures. The siliceous phillipsite preferred the larger cation more strongly for the Na-K system, and Na more strongly for the Na-Ca system than the aluminous phil-lipsite. Key W...