Clinoptilolite has been thotnght a zeolite which resembles to heulandite in crystal structure and is more alkalic in chemical composition. Clinoptilolite and heulandite are usually distinguished in their thermal behavior. By our present investigation, calcium rich clinoptilolite is proved to exist and its maximum value of Ca (+Mg)/Na+K attains to approximately 1/2. Consequently clinoptilolite is classified into three types; i.e. K-rich type, Na-rich type and Ca-rich type, by chemical composition. Following ion exchanges are supposed to take place.
Ca (Mg)_??_2 (Na, K)
CaAl_??_(Na, K) Si
(Na, K) Al_??_Si
Destruction of crystal structure of each type Uy heating treatment is also investigated. The Ca-rich type is destructed by heating at 400°C, and the Na-rich types at 600°C, for 4 hours, respectively without transforming into “heulandite B”. The difference of destructive temperature is possibly caused by different ion ratio of Al/Si in their frameworks. Usually Ca-rich type is easily destructed, for it is also Si-poor as a result of the ion exchange CaAl→(Na, K) Si.