Possible Structures related to Mordenite

Abstract

MEIER¹ has recently given a structure for the fibrous aluminosilicate mordenite, containing strongly bonded chains of SiO₄ or AlO₄ tetrahedra. The chains, which have the unusual feature of containing a proportion of five-membered rings, are linked laterally to form a three-dimensional framework. All apical oxygen atoms are shared between two tetrahedra. In addition Meier and Gottardi²have shown that an alternative side linking of the same chains can account for the structure of dachiardite. This raises the question whether there are more structures which can be built from these chains. A little consideration will show that there is, in fact, an endless number. However, some arrangements involve rather improbable linkings and result in large unit cells, while others can be obtained only by distorting the natural bonding distances within the chains. If both these types are omitted there are just six structures which have undistorted chains and unit cells not encompassing more than four chains.