Magnetite-based pellets with large amounts of the additives olivine, calcite and quartzite were isothermally reduced in a tubular furnace to study and describe the reaction behaviour of the additive minerals in the pellets. The reduction was thermodynamically set to yield wüstite at three different temperatures: 900, 1000 and 1150°C. The mineralogical phases that had formed before and after reduction were studied by Scanning electron microscope and X-ray diffraction. The pellets with the different additives were different already before reduction due to different reaction behaviour during induration: The results showed that it was possible to identify the main reactions during reduction for pellets with all three additives. All but the very small quartzite particles remained unreactive in reducing atmosphere until they began to form a fayalitic melt at 1000°C. The calcium ferrites of the pellets with calcite reacted to form a porous calciowüstite already at 900°C. In the pellets with olivine, the magnesium, which had constrained into magnesioferrite pockets after induration, redistributed into the entire iron oxide structure at 900°C and also reacted with silica at 1000°C. The olivine core which had not reacted during induration did not appear to react in reducing conditions at temperatures of 1150°C and below. These reaction mechanisms have indicated a potential to reduce the required amounts of additives in the pellets.