The nucleation of nesquehonite (MgCO3 center dot 3H(2)O) in MgCl2-Na2CO3 system with and without the addition of NaCl was studied within a supersaturation range of 1.06-1.48 at 288.15-308.15 K. The supersaturation (S) of MgCO3 center dot 3H(2)O was exactly calculated by aqueous (H+ ion) model through OLI platform. The conductivity method was applied in this experiment to determine the induction period of MgCO3 center dot 3H(2)O. The effects of temperature, supersaturation, and presence of additive (NaCl) on the induction period of MgCO3 center dot 3H(2)O were studied experimentally. As expected from theory, it was found that the induction period decreases when either temperature or supersaturation increases. The induction period was prolonged by adding NaCl in solutions at a constant supersaturation. From the dependence of the induction period on temperature and supersaturation, it was possible to distinguish between the homogeneous and heterogeneous nucleation mechanisms. At last, the activation energy (E-act) for MgCO3 center dot 3H(2)O crystallization and the interfacial tension between MgCO3 center dot 3H(2)O and aqueous solutions of homogeneous (gamma(S,hom)) and heterogeneous (gamma(S.het)) nucleation were calculated from measurements of the induction period for the MgCO3 center dot 3H(2)O nucleation with and without the addition of NaCl. (C) 2010 Elsevier B.V. All rights reserved.