Gibbs energies of formation for hydrocerussite [Pb(OH) 2 . (PbCO 3 ) 2 (S)] and hydrozincite [Zn(OH) 2 ] 3 . (ZnCO 3 ) 2 (S)] at 298 K and 1 bar from electrochemical cell measurements

New values are reported for the Gibbs energies of formation from the elements for hydrocerussite Pb(OH) 2 · (PbCO 3 ) 2 and hydrozincite [Zn(OH) 2 ] 3 · (ZnCO 3 ) 2 . These ΔG 0 f values were obtained from electrochemical cells without liquid junction. We determined ΔG 0 f [Pb(OH) 2 · (PbCO 3 ) 2 (S)] = -1699.8 ± 1.6 kJ/mol for hydrocerussite and ΔG 0 f ([Zn(OH) 2 ] 3 · (ZnCO 3 ) 2 ) = -3163.3 ±4 kJ/mol for hydrozincite. These results allow future electrochemical cell experiments to be performed to determine the ΔG 0 f values of other hydroxycarbonate minerals using either the Pb amalgam-hydrocerussite or the Zn amalgam-hydrozincite as reference electrodes. These reference electrodes provide a strategy for establishing Gibbs energies for phases with two different anions, which are geochemically interesting but difficult to study experimentally.