DYNAMICS OF DEHYDRATION IN STILBITE-TYPE STRUCTURES - STELLERITE PHASE-B

Between 200° C and 400° C stellerite (Ca8Al16Si56O144×58H2O) exists as a collapsed phase B which very rapidly transforms, upon partial rehydration at room conditions, into a more stable phase C. After a considerably longer period of rehydration phase C transforms into a phase with cell parameters similar to those of the natural phase. Phase B results from a rotation of the fundamental structural unit and the consequent lowering of the symmetry from Fmmm to Amma. In stellerite B, as in barrerite B and C, the aluminosilicate framework is interrupted by the statistical breaking of an oxygen bridge. In this case however the resulting hydroxyl positions are not symmetrically equivalent and therefore enjoy full freedom. This explains the different thermal behaviours of stellerite and barrerite and allows one to formulate hypotheses on the dehydration dynamics of stilbite. © 1978 Springer-Verlag.