High-pressure and high-temperature Raman spectroscopy of end-member garnets; pyrope, grossular and andradite

The effect of P <= 22 GPa and T (<= 1300 K) on the Raman spectra has been measured on three natural garnets approaching end-member composition. All Raman modes increase or decrease linearly with P and T, respectively. Generally the high-frequency modes (800-1000 cm (super -1) ) have larger shifts than those lying below 650 cm (super - 1) . For garnets and olivines correlations between the mean frequency shift and crystal bulk modulus, are found for the bending modes of SiO (sub 4) polyhedra and lattice modes, in contrast to minerals in which the dominant compression measurement is polyhedral tilting (e.g. quartz and perovskite) which do not follow the orthosilicate trend.