Chabazite, gmelinite, levynite and erionite form a group of porous crystals which exhibit certain similarities. Structures have previously been proposed for the anionic frameworks of chabazite,5 gmelinite 5 and erionite.8 A structure is now proposed for levynite. On the basis of the crystallographic data, diffusion anisotropy and molecular sieve behaviour of the four types of framework have been examined and the channel systems described and compared.

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A synthetic zeolite having the offretite structure free of faulting has been examined by X-ray powder photography and electron micrography. The distribution of cations in the structure has been considered and forms enriched in various cations have been examined from the viewpoint of molecule sieving. This property of unfaulted offretite can be regulated according to the size of cation introduced into the main channels.

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