Process for manufacturing alpha alumina from dispersible boehmite

A process for the production of alpha alumina which comprises providing a starting material which is an aqueous dispersion in which the dispersed phase consists of boehmite having a dispersibility of less than 70% and acidifying the dispersion to a pH of from 2 to 3 by adding acid in sufficient quantity to lower the pH to the above level but insufficient to cause the alumina compound to dissolve completely, then subjecting the dispersion to a hydrothermal treatment by heating it under an autogenous pressure of from about 10 to 15 atmospheres at a temperature of from about 150.degree. to 200.degree. C. for a time of from 0.15 to about 8 hours so as to produce a colloidal boehmite with a dispersibility of at least 95%, adding seed material effective to promote the formation of alpha alumina, and drying and sintering to form alpha alumina particles with a Spot Index reduced to less than 50% of the figure obtained by forming the alpha alumina from the untreated boehmite starting material without the hydrothermal treatment.