Moving towards higher frequencies, there are several other bands in the IR and Raman spectra of AlPO 4 -H3 that have no counterpart in the spectra of AlPO 4 -C, e.g. Raman-active modes at 597 cm -1 , 639 cm -1 , 663 cm -1 , as well as several IR-or (weakly) Raman-active modes between 800 and 1000 cm -1 (indicated by asterisks in Figure ). An analysis of the displacement patterns shows that these modes are primarily associated with librations of the H 2 O molecules, sometimes coupled to internal deformations of the PO 4 tetrahedra. This is in accordance with a previous IR and Raman spectroscopic analysis of variscite and metavariscite, where modes between ∼600 and 870 cm -1 were assigned to H 2 O librations . Finally, although there are significant differences in the spectra above 1000 cm -1 , all modes in this frequency range are due to P-O bond stretching vibrations, and therefore not directly related to the presence of AlO 6 octahedra. Frequency labels are included for modes that are discussed prominently in the text, whereas asterisks indicate modes that are mentioned summarily.