New stability constant data are presented for the minerals blixite, mendipite and the compound Pb 7 O 6 Cl 2 .2H 2 O at 298.2 K and P = 10 5 Pa. Mendipite is in fact a metastable phase at this temperature, being thermodynamically stable under the appropriate conditions at temperatures above about 29°C Kinetic influences are of some significance with respect to the sequence of formation of solid phases in the PbO-HCl-HH 2 O system, and these have been elucidated for some important reactions. Penfieldite and fiedlerite appear to be metastable phases at all temperatures at 10 5 Pa. The results have been used to reassess the conditions of formation of the lead(II) oxy- and hydroxychloride phases that are known to form as minerals and as corrosion products of lead-containing artefacts. The effect of CO 2 on the system is also described.
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Edwards et al. (1992) studied this question.
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