in order to give a deeper insight into the cracking of the Verneuil corundum boules, several samples of different colors and from different industrial sources have been analyzed by means of white beam synchrotron radiation X-ray diffraction topography (WB-SR-XRDT) and PBC analysis (Hartman and Perdock theory). The cracking occurs along an irregular surface containing the elongation axis of boules, and the WB-SR-XRDT analysis shows that this surface is nearly parallel to the {1(2) over bar 0} crystallographic planes. Following Hartman and Perdock theory, these planes form F-planes with a high density of PBC directions: 3 PBC directions-[211], [210] and [(4) over bar(2) over bar1]-have been recognized as parallel to the 120 plane. The 102 planes that are normal to the cracking surface of boules are F-planes too, but they show a lower bond density per unit area with respect to the 120 planes. Ab initio calculations show that these planes have lower surface energies with respect to other hk0 planes, such as {100} and {010}. (C) 2002 Elsevier Science B.V. All rights reserved.