The heat capacities of phlogopite and paragonite have been measured from 5 to 1000 and 800 K, respectively, by combined cryogenic-adiabatic and differential scanning calorimetry. At 298.15 K (25°C) the molar heat capacity, CP∘⁠, and the entropy change, S298∘−S0⁠, are 355.1 ± 1.1 and 315.9±1.0 J/(mol · K) for phlogopite and 321.5±1.0 and 277.1±0.9 J/(mol · K) for paragonite.

For the temperature range 298.15 to 1000 K, the molar heat capacity of phlogopite in J/(mol · K) is represented by
Cpo=872.13−0.07725T+3.575×105T−2−8600.6T−0.5(±0.7 percent).
For the temperature range 298 to 800 K, the molar heat capacity of paragonite is represented by
Cpo=688.44+0.03627T−1.8604×106T−2−5816.1T−0.5(±0.5 percent).
We have combined our calorimetric results with data from the P–T equilibrium studies of Chatterjee (1972) for the reaction
paragonite + quartz = analbite + andalusite + steam
and with those of Holland (1979) for the reaction
paragonite = jadeite + kyanite + steam

to derive improved values for the enthalpy and Gibbs free energies of formation of paragonite. On the assumption that the paragonite formed in the equlibrium studies is disordered, in accord with crystal structure studies, our values are −5933.07±4.70 and −5557.88±4.70 kJ/mol for ΔHf,298o and ΔGf,298o⁠, respectively. If, however, paragonite is ordered, the correct values are −5949.33±4.60 and −5568.46±4.60 kJ/mol.

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