Structural and spectroscopic study of well-developed crystals of parahibbingite, Beta-Fe2(OH)3Cl, formed from terrestrial weathering of the Muonionalusta iron meteorite

Parahibbingite [beta-Fe2(OH)3Cl], a new mineral recently described from ultramafic rocks in the Bushveld Complex, South Africa, has been found to form millimetric well-developed crystals as a terrestrial weathering product of the Muonionalusta iron meteorite. The mineral, initially identified by means of Raman spectroscopy, was found in a small cavity within a crust of rust on a granitic rock fragment that was in direct contact with the alteration crust of a meteorite specimen, collected in the Kitkiöjärvi area, Sweden. Its crystal structure was refined from single-crystal X-ray diffraction data (R1 = 0.0331) in the space group R3m [a = 6.9362(4), c = 14.673(1) Å and V = 611.35(7) Å3 for Z = 6], thus confirming the structural model of synthetic beta-Fe2(OH)3Cl. It consists of a network of octahedrally coordinated Fe2+ atoms alternately arranged in triangular and Kagomé layers, stacked along the c axis. The H atom position was determined, showing O-H---Cl bonds, which provides a further link between layers. Parahibbingite is found to be not only an important constituent of the corrosion system of archaeological iron artefacts but can also play an important role as an alteration product of iron meteorites.