The surface microstructure of a polished Ir sample during isothermal heat treatment at 1373 K in air was characterized. Various surface morphologies including triangular pits and terraces, "pyramid"-like plateaus and striated edges were observed. Changes in surface geometry were highly dependent on the original grain orientation. Most grains were confirmed to possess or partly exhibit a geometric configuration of {1 1 1} faceting habit, while periodic bond chain (PBC) vectors played an important role in determining the ultimate surface morphology. The mechanism and process of how these distinct surface morphologies formed are discussed. (C) 2011 Elsevier B.V. All rights reserved.