Pressure dependence of Raman spectra from the garnet end‐members pyrope, grossularite and almandite

Abstract

The synthetic end‐member garnets pyrope, grossularite and almandite were studied at high pressures using Raman spectroscopy. Previous vibrational mode assignments for these garnets were modified to account for the splitting of some degenerate modes at high pressures and other observed pressure effects. The band widths indicate that residual stresses are present in the garnets at ambient conditions and that these diminish as they approach their formation pressures. No pressure‐induced phase changes were observed and mode‐gruneisen parameters calculated from the pressure shifts and the bulk modulus indicated that these garnets all behave similarly with increasing pressure. The Raman bands varied linearly with increasing pressure and a slope of 0.40 ± 0.01 cm−1 kbar−1 was obtained for the most intense A1g mode of each garnet. These observations allow us to predict that natural aluminosilicate garnets, included in diamonds or other transparent minerals, may be used to monitor in situ pressures up to 150 kbar, provided that a Raman spectrum can be obtained from a similar garnet at ambient conditions. Show more