An experimental investigation of the system MgO-SiO 2 -H 2 O-CO 2

Equilibrium reactions of this system were experimentally investigated at pressures to 7000 bars and temperatures to 660 degrees C. Serpentine can coexist only with a CO ~2~ -poor fluid, and the lower stability limits of forsterite and talc are determined; talc is a metamorphic mineral at high pressures. The upper and lower stability limits of talc + magnesite are also determined and set limits on the temperature of formation of talc-bearing magnesite deposits and magnesite-bearing talc deposits. The conditions of origin for a number of types and specific localities of magnesite deposits are discussed in the light of these experimental studies.