  In the literature on the w{\"u}stite/magnetite transformation, there are two
distinct values of the enthalpy and entropy terms of the equilibrium between
these two oxides. The formalism established previously for the calculation of
thermodynamic properties of w{\"u}stite is taken as well as the adjustment of
the boundary between the respective domains. A first-order transformation of
the magnetite is demonstrated at 1 433 K or 1 160{\textdegree}C where the
change in the reference enthalpy is -9 990 J.mole-1 at heating, with the
corresponding entropy change being-6.89 J.K-1. . mole-1. The approximate
determination of enthalpy vs temperature is made for both varieties of
magnetite. Two values of the molar heat content are deduced, with which a
direct experimental value can be compared.
