GaN crystals grown from solution and vapor phase show pronounced facetting. In order to explain the occurrence of the facets, Jackson's a-factor is determined for the III-nitrides under various growth conditions. Jackson's theory confirms that for all growth methods presently used, the a-factor is so large that facetting must occur. For the special case of low-pressure solution growth (LPSG) the a-factor is larger than 6 for a (0 0 0 1) growth surface. By applying published results of density functional theory (DFT) it is shown that an unreconstructed growth interface has to be expected in solution growth techniques. This is also expected for a- or m-plane surfaces of GaN. (c) 2006 Elsevier B.V. All rights reserved.