Elasticity and sound velocities of polycrystalline grossular garnet (Ca3Al2Si3O12) at simultaneous high pressures and high temperatures

•Velocities of grossular garnet to 10 GPa and 1000 K.•Ultrasonic interferometry in conjunction with synchrotron X-radiation.•Garnet elasticity not sensitive to Ca content except for shear modulus.

The elastic wave velocities of a dense polycrystalline specimen (99.7% of theoretical density) of synthetic grossular garnet (Ca3Al2Si3O12) were measured to pressures of ∼10 GPa and temperatures of 1000 K by transfer-function ultrasonic interferometry in conjunction with energy-dispersive synchrotron X-radiation in a deformation DIA-type cubic-anvil apparatus. The calculated elastic bulk (Ks) and shear (G) moduli data were fitted to functions of Eulerian strain to 3rd order, yielding the zero-pressure values [Ks = 171.2 (8) GPa; G = 107.4 (2) GPa] and their pressure derivatives [(∂Ks/∂P)T = 4.47 (2); (∂G/∂P)T = 1.29 (5)]. The temperature dependences of the elastic moduli obtained from linear regression of entire P–T–Ks and P–T–G data are: (∂Ks/∂T)P = −1.38 (3) × 10−2 GPa/K and (∂G/∂T)P = −1.28 (2) × 10−2 GPa/K. These results together with those from previous studies for garnets with varying compositions suggest that most of the thermo-elastic properties of garnet are insensitive to grossular content, with the exception of the shear modulus, which significantly depends on the calcium content.