The surface of an aluminosilicate ceramic was transformed to a corundum layer of high specific surface area by heating at 1300degrees-1450degreesC in a controlled reducing atmosphere. This procedure selectively reduced and volatilized the silica of the glass and mullite, and the alumina of the mullite formed a layer of corundum crystals with a thickness of less than or equal to20 mum and a specific surface area of less than or equal to16 m(2)/g. Specific surface area remained stable at 10.5 m(2)/g after prolonged heating at 1300degreesC in air, and at 8.5 m(2)/g at 1450degreesC. These materials are well suited for use as catalyst supports in applications such as catalytic combustion at temperatures in this range.