Atomic force microscope (AFM) has been used to investigate the mechanism of gibbsite crystallization on all the morphologically important faces. Growth on single crystal faces has been observed by a series-of ex situ experiments, in which the same area was repeatedly located and imaged after growth had occurred in synthetic solution. At the same supersaturation level and temperature, the ex situ experiments have revealed a variety of growth modes: (1) Continuous birth and spread on a flat surface, the nuclei forming as approximately circular features that develop into elongated features, indicating anisotropic growth, followed by restoration of the flatness of the original area after further growth. (2) Step growth followed by rough growth on a surface that contains growth hillocks. (3) Two-dimensional. nucleation on a surface that contains a surface defect (tilt boundary). The results are used to establish a clearer picture of the growth mechanism of gibbsite, and the effect of the seed surface structure. On the prismatic faces of gibbsite, steps parallel to the (0 0 1) face and block formation were imaged. Step growth Was observed in both the [0 0 1] direction and parallel to the (0 0 1) plane. No nucleation was observed, and no emergent screw dislocations have been resolved. (C) 2003 Elsevier B.V. All rights reserved.