Low-temperature heat capacities of CaAl₂SiO₆ glass and pyroxene and thermal expansion of CaAl₂SiO₆ pyroxene

Low-temperature heat capacities (5–380 K) have been measured by adiabatic calorimetry for synthetic CaAl₂SiO₆ glass and pyroxene. The values of $S298.15∘−S0∘$ 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 parameters were measured for CaAl₂SiO₆ pyroxene by means of a Nonius Guinier–Lenne powder camera. The mean coefficient of thermal expansion is α_v = 2.78 × 10⁻⁵/°C in the temperature range 25° to 1200°C.