Application of freezing-point depression theory to experimentally-determined melting relations of anorthite in binary systems with silica, orthoclase, leucite, albite, wollastonite, and diopside yields results which are consistent with an enthalpy of fusion for anorthite of 81000 J/mol, the best estimate of Robie et al. (1978). The calculations are made using the 8-oxygen model of silicate melts suggested by Burnham (1975). They also incorporate solid-solution data among anorthite, quartz, and orthoclase. All temperatures are converted to the International Practical Temperature Scale of 1968.
The binary silicate systems studied do not appear to mix ideally, but they may be described by regular solution theory. The deviations from ideal behavior are related to the ionic potential of the cations.