Iron corrosion in archaeological context: Structural refinement of the ferrous hydroxychloride β-Fe2(OH)3Cl

Ferrous hydroxysalts are found in corrosion layers of archaeological ferrous objects extracted from oxygen-poor environments. The structure of synthetic and natural β-Fe2(OH)3Cl was investigated by X-ray absorption spectroscopy and X-ray diffraction. The local environments of Cl− and Fe2+ were precisely determined showing the same structure around Cl− and Fe2+ atoms whatever the natural or synthesized phase. The crystalline structure was refined confirming the rhombohedral unit cell and R-3m space group. However slight differences observed for the structural parameters and on XRD patterns suggested different crystallite size, strain effects and the influence of the crystallization process.