Previous experimental studies and observations from natural crystals indicate that there is a miscibility gap between ulvospinel and magnetite. The position and shape of the miscibility gap are poorly understood. Magnetite and magnetite- ulvospinel minerals re important carriers of permanent rock magnetism. The location of the miscibility gap for each composition with respect its Curie Temperature and the investigation o the changes in the magnetic properties associated with changes in mineralogy due to unmixing, coarsening, and microstructural development will provide new insights into the links between exsolution and lock magnetism.