Abstract
The high-pressure elastic properties of single-crystal andradite garnetCa3Fe23+Si3O12 were determined by Brillouin scattering to 11 GPa. The pressure dependence of theelastic stiffness constants and aggregate bulk and shear moduli were obtained byinversion of the data to finite Eulerian strain equations. The inversion yieldsC11 = 286.7 ± 0.6 GPa,C12 = 88.6 ± 0.6 GPa,C44 = 83.8 ± 0.3 GPa,K0S = 154.5 ± 0.6 GPa,G0S = 89.7 ± 0.4 GPa, , and . Both individual and aggregate elastic moduli define nearly linear modulus–pressuretrends. The elastic anisotropy of andradite garnets increases weakly in magnitude withcompression. Previous studies of the high-pressure elasticity of andradite garnet are highlydiscrepant, with reported pressure derivatives of the bulk modulus varying by 46% andpressure derivatives of the shear modulus varying by 253%. We are able to provideplausible explanations for these discrepancies. In particular, differences between previousx-ray diffraction data and a static compression curve constructed from our Brillouin datacan be attributed to the effects of non-hydrostatic stresses on the x-ray data.
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