The heat of formation of MgB2 was determined calorimetrically from the reaction of the boride with S at 1100C. It was found to be equal to 12.30kcal/mol.

Mg-B System and the Determination of the Enthalpy of Formation of Magnesium Borides. S.M.Ariya, M.P.Morozova, G.A.Semenov, G.A.Rybakova: Zhurnal Fizicheskoi Khimii, 1971, 45[1], 181-2