The crystal chemistry of natural zeolites

Abstract

This is a review of new achievements in the field of crystal chemistry of natural zeolites after 1983. There are two new zeolites, willhendersonite and perliaite, and two new frameworks, those of par-theite and goosecreekite; gobbinsite has the framework of gismondine, and gonnardite that of natrolite. Bikitaite has been shown to have a triclinic symmetry and an ordered (Si, Al) distribution. T-O-T angles of 180° are not present in dachiardite and in a variety of ferrierite. Edingtonite may be (Si, Al) ordered or not. Structural study of a number of exchanged chabazites has put some light on the gas absorption behaviour of this zeolite. Neutron diffraction studies led to location of hydrogen atoms in many zeolites; in natrolite, scolecite, thomsoni-te, edingtonite, bikitaite, the water molecules are well ordered, but this is true only to a lesser extent in other non-fibrous zeolites, like brewsterite, yugawaralite, laumontite, gismondine. The H.O distances found to date are among the longest found in crystalline hydrates and indicate that the hydrogen bonds formed between water molecules and framework oxygens are rather weak. A new computing method has been devised to deduce the Al-content of the tetrahedra of a framework from T-O distances and T-O-T angles, because the contents obtained via Jones’ linear relation are systematically too low. Newly assessed correlations between chemistry and genesis of zeolites raise intriguing problems on the possibility of explaining these correlations. © 1986 IUPAC