High-pressure behaviour of the zeolite phillipsite: an in situ single-crystal synchrotron diffraction study

Phillipsite is one of the most common natural zeolites, found in “closed” or “open” hydrologic systems. Its Si/Al tetrahedral framework contains two main channel systems: an 8-membered ring channel along [100] and an 8-membered ring channel along [010], which intersect each other [1]. In order to investigate the high-pressure behavior of phillipsite and its structural evolution at the atomic scale, we performed an in situ single-crystal synchrotron X-ray diffraction experiment up to 10 GPa, using a nominally penetrating pressure-transmitting fluid (methanol:ethanol:H2O=16:3:1 mix) [2] and a diamond anvil cell. The unit-cell parameters and the structure refinements within the P-range investigated show that: 1) phillipsite does not adsorb further H2O molecules from the pressure fluid; 2) the configuration of the extra-framework population changes with pressure, affecting the elastic behavior of the mineral; in particular, two distinct compressional regimes have been observed; 3) phillipsite is crystalline at least up to 10 GPa, and this is surprising if we consider its microporous nature; all the P-induced effects are completely reversible.