We have measured the relative enthalpy, HT-H300Kglass, and the heat capacities of CaMgSi2O6 (Di) stable liquid and glass; of KAISi3O8(Sa) stable and supercooled liquid and glass; of NaAlSi3O8 (Ab) liquid derived directly by melting solid albite; of crystalline, disordered albite itself; and of NaAlSiO4 (Ne) liquid and glass. We have also determined the effect of annealing at 981 K on the enthalpy of the glasses quenched from liquids at high temperature. This effect is relatively small, ranging from 0 to 1100 cal/mol. These data can be combined with published results on heats of vitrification and the heat capacities of solids to yield heats of fusion, in kcal/mol: Di 33.0±0.5 (1665 K); Ab: 15.0±0.5 (1373 K); Sa: 13.8±1.0 (metastable, 1473 K); and Ne: 11.7±0.5 (metastable, 1750 K).

Albite liquid prepared by melting of the crystalline phase has a heat capacity and relative enthalpy indistinguishable from those of a liquid produced by heating the glass. The enthalpy of crystalline, disordered albite (probably monoclinic) is equal to that predicted by heat capacity data collected below 1000 K for the triclinic phase by Hemingway et al. (1981). The liquid heat capacities of Ab and Sa (88.2 and 89.5 ca/mol · K) are nearly equal and are much lower than that for An liquid (113 cal/mol · K), suggesting that the latter undergoes greater structural changes, possibly depolymerization, with increasing T. The entropies of fusion of Ab and Sa (10.9 and 9.4 cal/mol · K) are similar, and much of the difference between these values and that for An (17.7 cal/mol · K) could be due to Al/Si order in crystalline An.

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