Dynamics of dehydration in stilbite-type structures; stellerite phase B

Stellerite [1319-24-0], Ca8Al16Si56O144· 58H2O, exists as a collapsed phase B at 200-400°, which transforms very rapidly upon partial rehydration at room conditions, into a more stable phase C. After a much 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 O bridge. The resulting OH positions are not sym. equiv. and therefore have full freedom. This explains the different thermal behaviors of stellerite and barrerite and permits formulation of hypotheses on the dehydration dynamics of stilbite [67338-75-4]