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Low-temperature heat capacities (5-330 K) have been measured by adiabatic calorimetry for synthetic CaAl2SiO6 glass and pyroxene. The values of S°298.15 - S°0 are 155.3 J/mol·K for the glass and 135.3 J/mol·K for the pyroxene. These entropies do not include zero-point contributions arising from configurational disorder. From an analysis of conflicting data bearing on the amount of Al/Si tetrahedral disorder in the pyroxene, we conclude that a small amount of tetrahedral short-range order probably exists.
High-temperature unit-cell parametersw ere measuredf or CaAl2SiO6 pyroxene by means of a Nonius Guinier-Lenne powder camera. The mean coefficient of thermal expansion is αv = 2.78 x 10-5/℃ in the temperature range 25° to 1200℃.