Spectroscopic investigation on the presence of hydroxyl in natural barrerite and in its collapsed phases

Barrerite, a zeolite with a stilbite-type framework, transforms on heating at 200-380 and at 380-450° into 2 new phases, called barrerite B and D, resp. After a few days, barrerite B rehydrates to barrerite C. In the B and C heat-collapsed phases, the aluminosilicate framework is interrupted by the statistical breaking of an O bridge, giving rise to 2 partially occupied face-sharing tetrahedrons. Near-IR diffuse reflectance spectra show the absence of hydroxyls in natural barrerite and the presence of hydroxyls in its heat-collapsed phases. These results confirm the hypothesis that the fourth vertex of the tetrahedrons, generated by the breaking of the O bridge, is a OH. The presence of OH-bands in phase D suggests for this phase, as in the B and C phases, the presence of interrupted O bridges.