The system CaCO 3 -SrCO 3 has been investigated at temperatures of 560 degrees C and 655 degrees C and pressures up to 13 kb. At constant temperature, orthorhombic mix crystals of CaCO 3 and SrCO 3 are stabilized at lower pressures as the SrCO 3 content increases. The amount of SrCO 3 in metamorphic aragonites (about one mole percent) is insufficient to cause a significant lowering of the pressure of the calcite-aragonite equilibrium. Substitution of MgCO 3 in calcite coexisting with aragonite-strontianite of a certain composition raises the equilibrium pressure (at constant temperature) until a maximum value is reached, at which calcite and aragonite-strontianite coexist with dolomite.

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