GIBBS ENERGIES OF FORMATION FOR HYDROCERUSSITE [PB(OH)(2)CENTER-DOT(PBCO3)(2)(S)] AND HYDROZINCITE ([ZN(OH)(2)](3)CENTER-DOT(ZNCO3)(2)(S)) AT 298 K AND 1-BAR FROM ELECTROCHEMICAL-CELL MEASUREMENTS

New values are reported for the Gibbs energies of formation from the e lements for hydrocerussite Pb(OH)(2).(PbCO3)(2) and hydrozincite [Zn(O H)(2)](3).(ZnCO3)(2). These Delta G(f)(0) values were obtained from el ectrochemical cells without liquid junction. We determined Delta G(f)( 0) [Pb(OH)(2).(PbCO3)(2) (s)] = -1699.8 +/- 1.6 kJ/mol for hydroceruss ite and Delta G(f)(0) {[Zn(OH)(2)](3).(ZnCO3)(2)} = -3163.3 +/- 4 kJ/m ol for hydrozincite. These results allow future electrochemical cell e xperiments to be performed to determine the Delta G(f)(0) values of ot her hydroxycarbonate minerals using either the Pb amalgam-hydrocerussi te or the Zn amalgam-hydrozincite as reference electrodes. These refer ence electrodes provide a strategy for establishing Gibbs energies for phases with two different anions, which are geochemically interesting but difficult to study experimentally.