[en] Seventy new measurements (Srsub(T)-Psub(CO₂)) of the solubility of strontianite were used to evaluate the equilibrium constant for the reaction SrCO₃(cr) = Sr²⁺(aq) + CO₃^2-(aq) between 2 and 91 deg C. An expression is given for the temperature dependence of the equilibrium constant. The log K of strontianite, the Gibbs energy, enthalpy and entropy of the reaction at 25 deg C are given. The equilibrium constants are consistent with an aqueous model that includes the ion pairs SrHCO₃⁺(aq) and SrCO₃⁰(aq) which were evaluated by potentiometric methods between 5 and 80 deg C. Expressions are also given for the equilibrium constant for the association reaction Sr²⁺(aq) + HCO₃^-(aq) = SrHCO₃⁺(aq), and for the association reaction Sr²⁺(aq) + CO₃^2-(aq) = SrCO₃⁰(aq). The results lead to reliable calculation of the aqueous speciation and solubility of strontianite in the system SrCO₃-CO₂-H₂O from 0 to more than 90 deg C. Literature data on the solubility of strontianite have been evaluated and compared with these results. Our new data for strontianite have been used in an evaluation of the thermodynamic properties of Sr²⁺(aq), SrCO₃(cr) and related compounds. Values are recommended for the standard enthalpy Gibbs energy and entropy,respectively, of Sr²⁺(aq). (U.K.)