Thermoelastic Equation of State of Monoclinic Pyroxene: CaMgSi2O6 Diopside

Abstract

We have conducted an in situ synchrotron x-ray diffraction study on a monoclinic pyroxene: CaMgSi2O6 diopside at simultaneous high pressures and high temperatures up to 8.2 GPa and 1280 K. A modified Rietveld profile refinement program has been applied to refine the diffraction spectra of low symmetry and multiple phases observed in energy dispersive mode. Thermoelastic parameters for diopside CaMgSi2O6 are derived by fitting the P-V-T data to the high-T Birch-Murnaghan equation of state. We obtained isothermal bulk modulus KTo=109.1 GPa with a pressure derivative of bulk modulus K′=∂K/∂P =4.84, temperature derivative of bulk modulus K = ∂K/∂T=−2.05×10′г GPa/K, volumetric thermal expansivity a = а + ЬT with values of a=2.32×10−5K−1 and b=1.88×10−8 K−2. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.