Raman spectra of phase transitions in analcime and leucite at high pressures

The behavior of natural analcime (Nidym, Siberian platform), its K- and Rb-forms, and natural leucite (Orvietto, Italy) was studied by Raman spectroscopy in a diamond anvil cell at pressures up to 47 kbar. Natural analcime exhibits three phase transition at 7, 20, and 37 kbar, the latter showing anomalies in the frequency region of the framework vibrations. Anhydrous K- and Rb-analcimes, containing cations in the water positions, and natural leucite exhibit similar high-pressure behavior with only one phase transition at about 22-26 kbar. These transitions are supposed to be of displacive and related to the distortions of secondary building units of the aluminosilicate framework, in particular, four-membered rings (we propose the geometry of such distortions), and to displacements of intrachannel cations and water molecules.