The molar enthalpies of solution of 2MgO (.) 2B(2)O(3) (.) MgCl2 (.) 14H(2)O in approximately 1 mol (.) dm(-3) aqueous hydrochloric acid (HCl) and of MgCl2.6H(2)O(s) in aqueous (approximately 1 mol (.) dm(-3) HCl + MgCl2 + H3BO3) at T = 298.15 K were determined. From a combination of these results with measured enthalpies of solution of boric acid (H3BO3) in HCl(aq) and of magnesium oxide (MgO) in aqueous (HCl + H3BO3) solution, together with the standard molar enthalpies of formation of MgO(s), H3BO3(s), MgCl2 (.) 6H(2)O(s) and H2O(1), the standard molar enthalpy of formation of -(8812 +/- 3) kJ (.) mol(-1) of 2MgO (.) 2B(2)O(3) (.) MgCl2 (.) 14H(2)O was obtained. Thermodynamic properties of this compound were also calculated by group contribution method. (C) 2003 Elsevier Ltd. All rights reserved.