Crystal structures of zeolites with the general formula CaAl₂Si₄O₁₂ · nH₂O

Abstract

The structures of chabazite, laumontite, and wairakite are analyzed using literature data with the aim of revealing their similar and dissimilar features. The framework of the three zeolites contain chains made up of alternating six-and four-membered rings. A distinguishing feature of chabazite is a network of oxygen-hydrogen bonds between intraframework oxygens (which link silicon (aluminum) atoms) and water molecules and between water molecules. A characteristic feature of laumontite is the ordered arrangement of the silicon and aluminum sites in the framework in the form of alternating aluminum and silicon layers. A distinguishing feature of wairakite is that there are no oxygen-hydrogen bonds between water molecules. The transition from the chabazite framework to the laumontite framework can be interpreted in terms of the ordering and displacement of aluminum and silicon atoms. In addition to the differences between the frameworks of laumontite and wairakite, which are attributable to the fact that these zeolites were formed at different temperatures and pressures, they differ in the relative arrangement of the water molecules and calcium atoms, which cannot be accounted for by different formation conditions.