A crystal structure for the souzalite/gormanite series from synchrotron powder diffraction data

In absence of suitable single crystal due to polysynthetic twinning, the crystal structure of a specimen in the souzalite/gormanite series (Fe, Mg) 3 (Al, Fe) 4 (PO 4 ) 4 (OH) 6 -2H O is determined ab initio from synchrotron powder diffraction data. The crystals belong to space group P 1, the cell is different from previously reported with a = 7.2223(1), b = 11.7801(1), c = 5.1169(1) A; α = 90.158(1), β = 109.938(1), γ = 81.330(1)°; V = 404.02(1) A 3 ; Z = 1. The structure consists of infinite chains of alternating [FeO 6 ], [MgO 6 ] and [AlO 6 ] octahedra sharing faces and/or edges. These chains are connected by corners with clusters of three corner-sharing [AlO 6 ] octahedra, forming octahedral layers which are interconnected by [PO 4 ] groups. A comparison with other minerals of similar composition and structure is made (dufrenite, burangaite).