Heat capacity from 12 to 305°K and entropy of talc and tremolite

The heat capacities of talc, Mg₃Si₄O₁₀(OH)₂, and tremolite, Ca₂Mg₆Si₈O₂₂(OH)₂, have been measured between 12 and 305°K. Smoothed values of heat capacity, entropy, enthalpy, and free energy are tabulated. At 298.15° K. the values of the thermodynamic functions are: talc, C_p°= 76.89 ± 0.23 cal. deg.^-1 mole^-1, S° = 62.33 ± 0.19 cal. deg.^-1 mole^-1, H° - H₀° = 11,206 ± 34 cal. mole^-1; tremolite, Cp° = 156.7 ± 0.6 cal. deg.^-1 mole^-1, S° = 131.2 ± 0.5 cal. deg.^-1 mole^-1, H° - H₀° = 23,335 ± 90 cal. mole^-1. From the equilibrium data of Bowen and Tuttle and the entropy of talc, the heat of formation of talc from MgO, SiO₂, and H₂O (liq.) is calculated to be ΔH°f₂₉₈ = -43.6 ± 1 kcal.