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 spectrosc opy in a diamond anvil cell at pressures up to 47 kbar. Natural analcime ex hibits three phase transition at 7, 20, and 37 kbar, the latter showing ano malies in the frequency region of the framework vibrations. Anhydrous K- an d Rb-analcimes, containing cations in the water positions, and natural leuc ite exhibit similar high-pressure behavior with only one phase transition a t about 22-26 kbar. These transitions are supposed to be of displacive and related to the distortions of secondary building units of the aluminosilica te framework, in particular, four-membered rings (we propose the geometry o f such distortions), and to displacements of intrachannel cations and water molecules.