Goethite, α-FeO(OH), from single-crystal data

Abstract

This is the first reported structure refinement of goethite, α-FeO(OH), on the basis of a single-crystal X-ray diffraction study. The structure of goethite, isostructural with diaspore, AlO(OH), and groutite, MnO(OH), can be described in terms of a slightly distorted hexa­gonal close-packed O-atom arrangement with Fe atoms occupying one-half of the octa­hedral inter­stices, and with all atoms located on mirror planes. There are two distinct O sites, O1 and O2, each bonded to three Fe atoms, with O2 additionally bonded to an H atom. The O2—H⋯O1 donor–acceptor distance in goethite is significantly longer than that in diaspore or groutite, indicating that the hydrogen bonding in goethite is the weakest of the three minerals. Analysis of refinement data for the three isostructural compounds reveals rigid-body thermal motion behavior of the octa­hedral groups.