Quartz heat capacity function

We have already stated that the a-[3 transition of quartz may be described as a A transition overlapping a first-order transition. The heat capacity function for the two polymorphs is thus different in the two stability fields, and discontinuities are observed in the H and S values of the phase at transition temperature T rans cf section 2.8). For instance, to calculate the thermodynamic properties of ]8-quartz at T = 1000 K and P = bar, we... 

Hemingway B. S., Krupka K. M., and Robie R. A. (1981). Heat capacities of the alkali feldspars between 350 and 1000 K from differential scanning calorimetry, the thermodynamic functions of alkali feldspars from 298.15 to 1400 K, and the reaction quartz + jadeite = albite. Amer. Mineral, 66 1202-1215. 

Cp is derived from enthalpies of Mosesman (J ) and White (2 ) whose data deviate from the adopted functions by -0.6 to +0.5% and +0.9 to 0.0%, respectively. White s deviations for cristobalite have a magnitude and trend similar to his deviations for quartz and vitreous siica. Data of Wietzel (3) for his sample prepared at 1600 C deviate by +3% at 673 K and +1.6% at 1973 K. C below 543 K is smoothly extrapolated to give the proper trend in the Gibbs energy, but the heat capacity at 298 K is not realistic. The entropy is calculated in a manner analogous to that of the enthalpy of formation. 

Table 3.2 Heat capacity of quartz as a function of temperature.

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