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.