In-situ synchrotron X-ray diffraction experiments were conducted using the MAX-III multi-anvil press of KEK on an omphacite (Di63Jd37), 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 KT0 = 126(1) GPa, an assumed pressure derivative of the bulk modulus KT′ = 4.0, a temperature derivative of the bulk modulus (∂KT/∂T)P = −0.015(4) GPa/K, and a volumetric thermal expansivity α = 2.2(1) × 10−5 K−1, when the equation of state of NaCl by Brown (1999) is adopted for the pressure scale. The derived KT0 value is consistent with the linear interpolations from KT0 values for diopside and jadeite in the literature.

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