Pure cerium oxide was produced via the sol-gel process, which allowed an investigation into the effect of thermal heat treatment on its crystallite shape and size. Transmission electron microscopy (TEM) and X-ray diffraction studies demonstrated that the actual crystallite shape changed with increasing calcination temperature. At a temperature of 850 degrees C, truncated octahedral crystallites were produced which display a greater a rea of close packed planes of cerium atoms on the surface, compared to those calcined at lower temperatures. Cerium oxide th at had undergone calcination at 850 degrees C is a Iso very effective as a glass-polishing medium. Because the calcination process effects both the shape of the crystal and its size at this temperature, it is proposed that polishing efficiency is predominantly determined by the higher incidence of cerium atoms th at can be presented to the glass surface.