The synthesis of refractory Mg-Al spinel aggegates from bauxites and magnesias was addressed by applying the alumina-magnesia-silica ternary equilibrium phase diagram as the fundamental basis. Four different alumina sources (bauxites) and four different magnesia sources were investigated. These were fired in, air through 1700degreesC and their reactions were monitored using X-ray diffraction. Evolution of their microstructure was observed by scanning electron microscopy. Initially, the periclase reacts with the free corundum of the bauxite to produce Mg-Al spinel. The periclase then reacts with the mullite in the bauxites to yield additional spinel and also some forsterite. Spinels were produced for all sixteen different raw-material combinations.