Gibbs energies of formation for hydrocerussite [Pb(OH) (sub 2) . (PbCO (sub 3) ) (sub 2) (S)] and hydrozincite [Zn(OH) (sub 2) ] (sub 3) . (ZnCO (sub 3) ) (sub 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) (sub 2) .(PbCO (sub 3) ) (sub 2) and hydrozincite [Zn(OH) (sub 2) ] (sub 3) .(ZnCO (sub 3) ) (sub 2) . These Delta G (super 0) (sub f) , values were obtained from electrochemical cells without liquid junction. We determined Delta G (super 0) (sub f) , [Pb(OH)2.(PbCO (sub 3) ) (sub 2) (s)] = -1699.8+ or -1.6 kJ/mol for hydrocerussite and Delta G (super 0) (sub f) , {[Zn(OH) (sub 2) ] (sub 3) .(ZnCO (sub 3) ) (sub 2) } = -3163.3 + or - 4 kJ/mol for hydrozincite. These results allow future electrochemical cell experiments to be performed to determine the Delta G (super 0) (sub 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.