Thermodynamic Properties and Phase Equilibria of the Secondary Copper Minerals Libethenite, Olivenite, Pseudomalachite, Kröhnkite, Cyanochroite, and Devilline

The thermodynamic properties of libethenite [Cu2(PO4)(OH)], olivenite [Cu2(AsO4)(OH)], pseudomalachite [Cu5(PO4)2(OH)4], cyanochroite [K2Cu(SO4)2 6H2O], kröhnkite [Na2Cu(SO4)2 2H2O], and devilline [CaCu4(SO4)2(OH)6 3H2O] were determined by a combination of acid-solution calorimetry (enthalpy of formation) and relaxation calorimetry (heat capacity and entropy). The calculated Gibbs free energies (in kJ mol–1) for these phases are –1229.3 ± 4.5, –848.7 ± 4.8, –2837.9 ± 10.8, –3441.4 ± 3.9, –2442.3 ± 3.6, –3843.2 ± 8.4, respectively. The phases studied were characterized by powder X-ray diffraction, infrared and Raman spectroscopy, and electron microprobe, as needed.