This paper presents detailed ex situ observations of spiral patterns on the (0 (1) over bar 0) face of the stable polymorph of the 7 alpha MNa steroid, using atomic force microscopy. In contrast to the opposite (0 10) face, which is rough, the (0 (1) over bar 0) face grows layer-wise involving steps down to monomolecular height. The growth spirals show symmetry induced interlacing, i.e. a regular splitting of d(010) steps into half height d(020) steps as a consequence of the 2(1) screw axis perpendicular to (0 (1) over bar0). In many cases differences in advancement rate of symmetrically non-equivalent layers and entropic repulsion leads to further step splitting generating steps of quarter unit cell height, d(040). The observed step orientations are identical to the strongest periodic bond chain directions within the thinnest growth layer thickness. The screw dislocations b = [0 10] at the spiral centers are marked by hollow cores. The edge dislocations ending on the same face do not reveal hollow cores. This is a consequence of their low stress fields, which is some 40 times smaller than that of the screw dislocations. (c) 2007 Elsevier B.V. All rights reserved.