Crystalline alumina particles are intimately mixed with a gaseous fuel, air and oxygen. The mixture is then ignited in a torch. Such blending of the powder with the combustible gas allows the alumina particles to be immediately heated to above their melting temperature and allows the particles to form into spheres. The spheres are then rapidly cooled to ambient temperature, providing high purity micron-sized polymorphic alumina spheres without the use of additives or special treatment.