Heat capacity and entropic mixing behaviour of the orthopyroxene solid solution (Mg,Fe)2Si2O6

Dachs, Edgar; Benisek, Artur; Cemič, Lado

doi:10.5194/ejm-37-909-2025

Articles | Volume 37, issue 6

https://doi.org/10.5194/ejm-37-909-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/ejm-37-909-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 37, issue 6

Research article

|

03 Dec 2025

Research article |

| 03 Dec 2025

Heat capacity and entropic mixing behaviour of the orthopyroxene solid solution (Mg,Fe)₂Si₂O₆

Edgar Dachs, Artur Benisek, and Lado Cemič

Cited articles

Aronson, M. C., Stixrude, L., Davis, M. K., Gannon, W., and Ahilan, K.: Magnetic excitations and heat capacity of fayalite, Fe₂SiO₄, Am. Mineral., 92, 481–490, https://doi.org/10.2138/am.2007.2305, 2007.

Benisek, A. and Dachs, E.: The accuracy of standard enthalpies and entropies for phases of petrological interest derived from density-functional calculations, Contrib. Mineral. Petr., 173, 90, https://doi.org/10.1007/s00410-018-1514-x, 2018.

Benisek, A., Dachs, E., Carpenter, M. A., Joachim-Mrosko, B., Vielreicher N. M., and Wildner, M.: Vibrational entropy of disordering in omphacite. Phys. Chem. Minerals, 50, 36, https://doi.org/10.1007/s00269-023-01260-7, 2023.

Berman, R. G. and Brown, T. H.: Heat capacity of minerals in the system Na₂O-K₂O-CaO-MgO-FeO-Fe₂O₃-Al₂O₃-SiO₂-TiO₂-H₂O-CO₂: representation, estimation, and high temperature extrapolation, Contrib. Mineral. Petr., 89, 168–183, https://doi.org/10.1007/BF00379451, 1985.

Bohlen, S. R., Metz, G. W., Essene, E. J., Anovitz, L. M., Westrum, E. F., and Wall, V. J.: Thermodynamics and phase equilibrium of ferrosilite: potential oxygen barometer in mantle rocks, EOS, 64, 350, 1983.

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Short summary

Orthopyroxenes are important rock-forming minerals. They are solid solutions mainly between an Mg and a Fe endmember. Their thermodynamic properties are needed to model the P–T–X paths of igneous and metamorphic rocks. Samples along this Fe–Mg binary were synthesized at 800 °C/1.5 GPa, and their heat capacity was measured using calorimetric methods. From these data, the entropies along the solid solution could be derived, and it was found that this solution behaves thermodynamically ideally.