The Crystal Structure of Lepidocrocite

The unit of structure, space group symmetry and detailed atomic arrangement of lepidocrocite are determined from x-ray data, and the existence and location of hydrogen bonds in the structure are established from considerations of interatomic distances. The orthorhombic lattice is end centered on (100), and has the axes a0 = 3.87A, b0 12.51A, and c0 = 3.06A. The space group is Vh17—Amam. The parameters are determined as uFe = —0.332, uO = +0.282, and uOH = +0.075. The structure is described as consisting of iron-centered oxygen octahedra joined by the sharing of edges into two-dimensionally infinite layers, with the successive layers held together by hydrogen bonds. The relationship between the diaspore-goethite structure and the böhmite-lepidocrocite structure is discussed from the standpoint of the coordination theory, and found to depend on two alternative ways of satisfying the electrostatic valence rule.