The heat capacities for magnesio-anthophyllite, diopside, synthetic enstatite, bronzite, and wollastonite were measured between 5 and 385 K by use of an adiabatic calorimeter. The entropy change S298oS0o, in J/(mol · K), is 538.9±2.7 for magnesio-anthophyllite [Mg6.3Fe0.7Si8O22(OH)2], 142.7±0.2 for diopside, 66.27±0.10 for synthetic enstatite (MgSiO3), 69.04±0.10 for bronzite (Mg0.85Fe0.15SiO3), and 81.69±0.12 for wollastonite. The heat capacity, CPo, for magnesio-anthophyllite, corrected to a composition of pure Mg-anthophyllite [Mg7Si8O22(OH)2], results in a S298oS0o value of 537.0±2.7 J/(mol·K). These results represent only the entropy calculated from the measured heat capacities. No configurational entropy was added.

Although our CPo values for diopside and wollastonite differ significantly from those of previous studies, especially at cryogenic temperatures, our entropies at 298.15 K are in close agreement with the commonly accepted values. Schottky heat capacity anomalies were observed below 25 K for magnesio-anthophyllite, diopside, and bronzite. The contribution of the magnetic entropy arising from the interaction of Fe2+ with the ligand field of the crystals is discussed.

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