Micro-Raman and micro-infrared spectra of the silicate and OH-stretching regions have been obtained from a well-characterized crystal of hydrous beta -Mg 2 SiO 4 containing approximately 2.6 wt.% H 2 O. Five distinct OH-stretching vibrations were observed in two separate spectral groupings. A Raman-active band at 3355 cm (super -1) and an infrared band at 3351 cm (super -1) comprise the first group; a Raman band at 3583 cm (super -1) and infrared band at 3596 and 3653 cm (super -1) make up the second group. These results are consistent with the incorporation of H into the O1 site. The apparent division of the OH-stretching bands into a group near 3330 cm (super -1) and a group near 3600 cm (super -1) is due to differences in the lengths of the hydrogen bonds to the nearest-neighbor oxygen atoms in the Mg2 and Mg3 octahedra. Relative intensities of the bands suggest that a majority of shorter, and hence, stronger hydrogen bonds are formed in the hydrated beta phase. Tentative assignments of the observed bands have been made by comparison with the corresponding spectra of anhydrous beta -Mg 2 SiO 4 .

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