Structural Classification of Zeolites

with a framework structure enclosing cavities occupied by large ions and water molecules, both of which have considerable freedom of movement, permitting ion-exchange and reversible dehydration. Because it is possible that materials with the typical physical properties of zeolites may not have framework structures, the above definition of a zeolite must be applied with caution. In order to identify the types of linkage in the zeolite structures, and to depict the structures on a two-dimensional paper surface, it has been necessary to resort to various simplifying devices in which tetrahedra and other structural units are denoted by symbols specifying their orientation. Such devices often lead to idealization of the structures, but the details can be found from the original references. For brevity, no attempt has been made to trace in detail the historical development of the determination of zeolite structures. However the references have been arranged in groups to correspond to the structural classification, and the historical sequence can be determined by inspection of the titles. The author wishes to pay tribute and make grateful acknowledgment to the following scientists who have contributed to this classification of zeolites: Dr. W. H. Taylor for his pioneering studies on analcime and the edingtonite group, Dr. D. W. Breck for ideas on the zeolites such as Linde A which are based on tetrahedra lying at the corners of convex polyhedra, Prof. R. M. Barrer and his group for their pioneering studies on molecular-sieve properties and associated structural effects, Drs. K. Fischer and W. M. Meier for their major contributions to the mordenite, gmelinite and gismondine groups, and also for the ABSTRACT