Stability of Carbonates in the System MgO-CO₂-H₂O

Published free-energy data on carbonates in the system MgO-CO₂-H₂O are largely either suspect or unavailable. This paper is a review and revaluation of information bearing on the stabilities of the carbonates nesquehonite, lansfordite, hydromagnesite, artinite, and magnesite. Whenever possible, several independent methods have been used to establish free-energy values. Free energies of formation from the elements at 25° C. and 1 atm. total pressure have been calculated from data on solubility, synthesis, thermal decomposition, heats of solution, and heats of combustion, as well as from geological occurrences. Selected free-energy values for magnesite and hydromagnesite differ substantially from published values. Stability diagrams based on preferred free-energy data are presented in summary, and appear to be essentially consistent with the low-temperature laboratory and geologic behavior of phases in this system.