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Compressibility and thermal expansion of hypersthene
Zhishuang Xu, Maining Ma, Baosheng Li, Xinguo Hong, Lin Han and Xiaoya Zhou

In-situ high-pressure and high-temperature X-ray powder diffraction has been employed to investigate the compressibility and volume thermal expansion of a naturally occurring hypersthene specimen (En0.540Fs0.424Ts0.028), using an externally heated diamond anvil cell (DAC) combined with synchrotron radiation up to 9.3 GPa and 673 K. The isothermal bulk modulus K0 = 120(5) GPa and its pressure derivative K′0 = 7.7(1.7) are obtained by analyzing room-temperature P-V data with the third-order Birch-Murnaghan equation of state (B-M EoS). The present study appears to be in agreement with previous data that the enrichment of Al stiffens the structure. The volume thermal expansion coefficient of hypersthene at ~6.6(2) GPa is determined to be α0 = 3.23(7) ×10–5/K, which is comparable to that of Fe-poor compositions, suggesting that the substitution of Fe for Mg has a weak influence on the thermal expansivity of orthopyroxene.

Keywords: hypersthene, high-pressure and high-temperature, diamond anvil cell, Equation of State, volume thermal expansion

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