THERMOELASTIC EQUATION OF STATE OF JADEITE NAALSI2O6 - AN ENERGY-DISPERSIVE REITVELD REFINEMENT STUDY OF LOW-SYMMETRY AND MULTIPLE PHASES DIFFRACTION

We report the first measurement of a complete set of thermoelastic equ ation of state of a clinopyroxene mineral. We have conducted an in sit u synchrotron x-ray diffraction study of jadeite at simultaneous high pressures and high temperatures. A modified Rietveld profile refinemen t program has been applied to refine the diffraction spectra of tow sy mmetry and multiple phases observed in energy dispersive mode. Unit ce ll volumes, measured up to 8.2 GPa and 1280 K, are fitted to a modifie d high-temperature Birch-Murnaghan equation of state. The derived ther moelastic parameters of the jadeite are: bulk modulus K = 125 GPa with assumed pressure derivative of bulk modulus K' = partial derivative K /partial derivative P = 5.0, temperature derivative of bulk modulus K = partial derivative K/partial derivative T = -1.65 x 10(-2) GPa K-1, and volumetric thermal expansivity alpha = a + bT with values of a = 2 .56 x 10(-5) K-1 and b = 0.26 x 10(-8) K-2. We also derived thermal Gr uneisen parameter gamma(th) = 1.06 for ambient conditions; Anderson-Gr uneisen parameter delta(To) = 5.02, and pressure derivative of thermal expansion <(o)over bar alpha>/(o) over bar P = -1.06 x 10(-6) K-1 GPa (-1). From the P-V-T data and the thermoelastic equation of state, the rmal expansions at five constant pressures of 1.0, 2.5, 4.0, 5.5, and 7.5 GPa are calculated. The derived pressure dependence of thermal exp ansion is: Delta alpha/Delta P = -0.97 x 10(-6) K-1 GPa(-1), in good a greement with the thermodynamic relations.