The crystal structure of perloffite

The structure of perloffite, ideally BaMn²⁺ ₂Fe ³⁺ ₂(PO₄)₃(OH)₃, has been solved and refined from single-crystal X-ray data collected on a Sr-bearing sample from the Spring Creek copper mine, near Wilmington, South Australia. A fragment of the crystal used for the collection of the X-ray intensity data was analysed by electron microprobe. The resulting unit formula is (Ba _1.00,Sr_0.03)_Σ1.03(Mn²⁺ _1.15,Fe²⁺ _0.76Ca_0.05Mg _0.02,Na_0.01)_Σ1.99(Fe³⁺ _1.94,Al_0.06)_Σ2.00(PO₄) _2.99(OH)_3.04. The structure is monoclinic, space group P2₁/m, a = 9.2425(18), b = 12.470(3), c = 5.002(1) Å, β = 100.19(3)°, V = 567.41(19) ų, Z = 2, and was refined to R ₁ = 4.71% for 1568 unique observed reflections. The X site is [11]-coordinated and is occupied by dominant Ba and minor Sr, with an <X-O> distance of 2.953 Å. The M1 site is octahedrally coordinated and is occupied by Mn²⁺ and Fe²⁺ plus minor Ca, Mg and Na with an observed <M1-O> distance of 2.208 Å. The M2 site is also octahedrally coordinated and is occupied by Fe³⁺ plus minor Al with a <M2-O> distance of 2.018 Å. Perloffite is isostructural with other members of the bjarebyite group. Edge-linked [M2₂O ₆(OH)₄] dimers link via corners to form chains along [010]. Chains are decorated with PO₄ tetrahedra and link in the a direction via [M1O₅(OH)] octahedra and (Ba,Sr) atoms to form a complex framework. The H2 atom hydrogen-bonds strongly to the O3 anion, providing additional linkage between chains.