The thermal decompn. under Ar of the boracites M3B7O13X (M = divalent metal ion, X = halogen ion or OH-) was studied by thermogravimetry (TG) and DTA for the compns. MgCl, MgOH, CrCl, CrBr, CrI, MnCl, MnBr, MnI, FeCl, FeBr, FeI, CoCl, CoBr, CoI, NiCl, NiBr, NiI, CuCl, CuBr, ZnCl, ZnBr, ZnI, CdCl, CdBr and DI. The lithium boracites Li4B7O12X (X = Cl and Br) were also studied. The stability of the boracites systematically decreases in the order MCl > MBr > MI. The most stable boracite is CrCl (1% wt. loss at 1242°) and the least stable one studied here is MgoH (1% wt. loss at 717°).