Abstract
The elasticities of six polycrystalline silicate garnets (almandine, grossular, pyrope, uvarovite, andradite, and Prp 25 Alm 56 Spe 19 ) have been experimentally studied at pressures up to 3.0 GPa using a phase comparison method with an ultrasonic interferometer in a liquid cell piston-cylinder apparatus. Complete elasticity data sets (P- and S-wave velocities, bulk moduli K s , shear moduli G, and their first pressure derivatives K S ′ and G ′) have been obtained for all six garnets, and are used together with an up-to-date compilation of garnet elasticity data to examine composition-elasticity systematics of garnets. Our results suggest that pyralspite and ugrandite have different relationships between bulk sound velocity (V ϕ ) and mean atomic weight (M 0 ), between Poisson’s ratio (σ) and density (ρ), and between G / K s and K s /ρ ratios. A large error may occur when the systematics are applied across different garnet groups.
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