Segelerite from the Mount Deverell variscite deposit, Western Australia. Hydrogen bonding and relationship to jahnsite

Abstract

The crystal structure of segelerite, Ca2Mg2Fe3+1.4Al0.6(PO4)4(OH)2(H2O)8, from the Mount Deverell variscite deposit, Western Australia, has been refined using single-crystal X-ray data to wRobs = 0.048 for 2082 unique reflections and all H atoms were located during the refinement. Cell parameters are a = 14.7772(2) Å, b = 18.7079(2) Å, c = 7.2424(1) Å, space group Pbca. The H-bonding scheme is described and compared to that for the combinatorial polymorph, jahnsite. The crystal structures of both minerals comprise heteropolyhedral slabs of composition [XM1Fe3+2(OH)2(PO4)4], that are linked together via corner-sharing of PO4 tetrahedra with isolated [M2(Op)2(H2O)4] octahedra. The structures d..