Raman spectroscopy of garnet-group minerals

The Raman spectra of the natural end members of the garnet-group minerals, which include pyrope, almandine and spessarite of Fe-Al garnet series and grossularite, andradite and uvarovite of Ca-Fe garnet series, have been studied. Measured Raman spectra of these minerals are reasonably and qualitatively assigned to the internal modes, translational and rotatory modes of SiO₄ tetrahedra, as well as the translational motion of bivalent cations in the X site. The stretch and rotatory Al_g modes for the Fe-Al garnet series show obvious Raman shifts as compared with those for the Ca-Fe garnet series, owing to the cations residing in the X site connected with SiO₄ tetrahedra by sharing the two edges. The Raman shifts of all members within either of the series are attributed mainly to the properties of cations in the X site for the Fe-Al garnet series and in the Y site for the Ca-Fe garnet series.