year of publication
Thermodynamic properties of two amphibole asbestos minerals were determined by the Bureau of Mines. The enthalpies of formation were determined by the hydrofluoric acid solution calorimetry method. Heat capacity measurements were made with an adiabatic calorimeter over the range of 5 to 315 K. High temperature enthalpies above 298 K were determined with a copper-block drop calorimeter to 852 K for amosite and to 902 K for crocidolite. Thermodynamic data determined for amosite of the composition(Fe+25.2766 Mg1.5209 Fe+30.12 Mn0.0825) (Si7.9163 Al0.0837 O22.0363)(OH)1.9637 are: S°298.15 = 168.8 ± 5 cal/deg-mole; ΔHf°298.15 (elements)= -2419.24 ± 2.95 kcal/mole; ΔHf298.15 (oxides) = -30.92 ± 2.47 kcal/mole; and ΔGf°298.15 = -2260.1 kcal. Corresponding data found for crocidolite of the composition (Na1 .9Ca0.1)(Fe+32.024 Fe+22.501 Mg0.475) (Si7.971 Al0.029 O22.095)(OH)1.905 are: S°298.15 = 161.1 ± 4 cal/deg-mole; ΔHf298.15 (elements) = -2433.56 ± 2.99 kcal/mole, ΔHf298.15 (oxides) = -87.69 ± 1.70 kcal/mole, and ΔGf298.15 = -2269.8 kcal.
Calorimetric values from this investigation were combined with other data from the literature to calculate the Gibbs energies of formation and equilibrium constants of formation over the temperature range of the measurements. Tables of enthalpies of formation and Gibbs energies of formation are given as a function of temperature both from the elements and the constituent oxides.