Red corundum crystals occur in a two meter wide zone in the gneisses 11 km northwest of Arendal, Southern Norway. The ordinary features of the crystals are described, and Universal stage work indicates that the "lamellar twinning" is due to alteration on cleavages. It is suggested as an alternative hypothesis to "lamellar twinning and parting parallel to the rhombohedron" that corundum possesses true cleavage and pseudo-twinning due to alteration.