The kinetics of the carbothermal reduction of magnetite to iron using carbon black was investigated in situ using the time-resolved X-ray powder diffraction synchrotron radiation technique for the case of magnetic microwave heating in an H-field maximum and conventional heating, respectively. The phase transformation sequence and the reaction kinetics were studied with respect to the case of heating in a microwave E-field maximum investigated earlier. The reduction to iron proceeds an order of magnitude faster when using microwaves. It proceeds at comparable rates in the E- and the H-field microwave heating, yet the reaction temperature is lowered to 770 degrees C in magnetic H-field microwave heating, compared to nearly 1200 degrees C for the E-field case. (c) 2012 Elsevier B.V. All rights reserved.