Thermal equation of state of omphacite

In-situ synchrotron X-ray diffraction experiments were conducted using the MAX-III multianvil press of KEK on an omphacite (Di(63)Jd(37)), for which Di = Ca(Mg,Fe)Si2O6 and Jd = NaAlSi2O6. Pressure-volume-temperature data were collected at up to 10 GPa and 1000 K. A fit to the high-temperature Birch-Murnaghan equation of state yielded an isothermal bulk modulus K-70 = 126(1) GPa, an assumed pressure derivative of the bulk modulus K-T' = 4.0, a temperature derivative of the bulk modulus (partial derivativeK(T)/partial derivativeT)(p) = -0.015(4) GPa/K, and a volumetric thermal expansivity alpha = 2.2(1) x 10(-5) K-1, when the equation of state of NaCl by Brown (1999) is adopted for the pressure scale. The derived K-T0 value is consistent with the linear interpolations from K-T0 values for diopside and jadeite in the literature.