Anew synthetic method of szaibelyite (2MgO.B2O3.H2O) has been reported. The enthalpy of solution of 2MgO.B2O3.H2O in 2.9842 mol dm(-3) HCl (aq) was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in 2.9842 mol dm(-3) HCl (aq) and of MgO in (HCl + H3BO3) solution, together with the standard molar enthalpies of formation of MgO (s), H3BO3 (s), and H2O (1), the standard molar enthalpy of formation of -(2884.36 +/- 1.82) kJ mol(-1) of 2MgO.B2O3.H2O was obtained. (C) 2003 Elsevier B.V. All rights reserved.