During the pyroconsolidation of magnetite pellets in an aerobic atmosphere, the mineral practically oxidizes in the beginning stages of the process. However, as the temperature increases, the hematite dissociates into magnetite. The temperature at which this phenomena occurs depends on the additives present and is significantly lower than that corresponding to pure magnetite. In this paper a series of magnetite pellets were formed, varying the alkalinity (CaO + MgO)/(SiO2 + Al2O3) from 0.4 to 1.9, and the MgO/CaO ratio from 0.12 to 1.3. The pellets were pyroconsolidated at temperatures ranging from 1050 to 1350°C. Pellet structure was determined and analyzed using electron microscopy. The influence of additives and gangue composition was studied at the hematite disassociation temperature.