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(PO4)4(OH)6-2HO is determined ab initio from synchrotron powder diffraction data. The crystals belong to space group P1, the cell is different from previously reported with a = 7.2223(1), b = 11.7801(1), c = 5.1169(1) Å; α = 90.158(1), β = 109.938(1), γ = 81.330(1)°; V = 404.02(1) Å3; Z = 1. The structure consists of infinite chains of alternating [FeO6], [MgO6] and [AlO6] octahedra sharing faces and/or edges. These chains are connected by corners with clusters of three corner-sharing [AlO6] octahedra, forming octahedral layers which are interconnected by [PO4] groups. A comparison with other minerals of similar composition and structure is made (dufrénite, burangaite).

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