Glasses and crystals of compositions MgCaSi2O6, CoCaSi2O6 and NiCaSi2O6 were studied by high temperature solution calorimetry, x-ray diffraction, and pycnometry. These data were combined with trace element distribution data to obtain values for ΔAG0, ΔH0, ΔS0, and ΔV0 for M-Mg exchange reactions. Enthalpies of vitrification increase in the order Co, Mg, Ni as do volumes of vitrification and apparent melting points. The mixing of Co and Mg, Ni and Mg, and Co and Ni is almost ideal in crystals and glasses, with small negative heats of mixing and small volume changes. The exchange reactions MgCaSi2O6 (xl) + MCaSi2O6 (liq) = MgCaSi2O6 (liq) + MCaSi2O6 (xl) are exothermic for Ni and endothermic for Co. The volumes and entropies of the exchange reaction are small.
ASJC Scopus subject areas
- Geochemistry and Petrology