Corundum (Al2O3) crystals with a unique form have been successfully synthesized by the evaporation of MoO3 flux at 1100°C. The grown crystals had a black color, and were up to 1.6×1.2 mm in size. Their form was a truncated bipyramidal tetradecahedron, bounded by twelve well-developed {1123} faces and two {0001} faces of sexangle. The sizes of the grown crystals were dependent on the solute contents. In this study, not Fe and Ti but Mo as a flux was found to be responsible for the characteristic black color.
