Phase Equilibrium in the System Calcite-Aragonite

Abstract

The equilibrium curve for two of the phases of CaCO3, calcite-aragonite, has been determined as a function of temperature and pressure over the range 25–80°C and several thousand kg/cm2, using the electrical conductivity of aqueous solutions of each form. Aragonite is proved to be the high pressure modification. From the determined equilibrium curve, various thermodynamic quantities are obtained in a more accurate fashion than previously possible. All normal natural occurrences of aragonite must be due to metastable formation rather than equilibrium, since the geothermal gradient lies completely in the calcite field.