Thermodynamics of diopside, anorthite, pseudowollastonite, CaMgGeO4, olivine, and akermanite up to near the melting point

To provide a better thermodynamic description of premelting, the heat capac ities of diopside, anorthite, pseudowollastonite, akermanite, and CaMgGeO4 olivine have been determined from drop calorimetry measurements performed u p to temperatures approaching the melting point. With the onset of premelti ng defined as the temperature at which the heat capacity begins to increase sharply, the premelting intervals of these minerals range from 80 to 250 K . Of the five compounds, pseudowollastonite exhibits the widest interval an d akermanite the lowest. Enthalpies of premelting range from 7 to 22% of th e reported enthalpies of fusion. Correspondingly, the entropies of premelti ng vary from 5.4 to 18 J mol(-1) K-1 and are consistent with temperature-in duced mobility of cations as a general premelting mechanism.