The crystal structure of perloffite

The structure of perloffite, ideally BaMn2+ 2Fe3+ 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 (Ba1.00,Sr0.03)Σ1.03(Mn2+ 1.15,Fe2+ 0.76Ca0.05Mg0.02,Na0.01)Σ1.99(Fe3+ 1.94,Al0.06)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) Å3, 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 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 distance of 2.208 Å. The M2 site is also octahedrally coordinated and is occupied by Fe3+ plus minor Al with a distance of 2.018 Å. Perloffite is isostructural with other members of the bjarebyite group. Edge-linked [M22O6(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.P. Elliott and A.C. Willi

The crystal structure of gatehouseite

The crystal structure of the manganese phosphate mineral gatehouseite, ideally Mn2+5(PO4)2(OH)4, space group P212121, a = 17.9733(18), b = 5.6916(11), c = 9.130(4) Å, V = 933.9(4) Å3, Z = 4, has been solved by direct methods and refined from single-crystal X-ray diffraction data (T = 293 K) to an R index of 3.76%. Gatehouseite is isostructural with arsenoclasite and with synthetic Mn2+5(PO4)2(OH)4. The structure contains five octahedrally coordinated Mn sites, occupied by Mn plus very minor Mg with observed distances from 2.163 to 2.239 Å. Two tetrahedrally coordinated P sites, occupied by P, Si and As, have distances of 1.559 and 1.558 Å. The structure comprises two types of building unit. A strip of edge-sharing Mn(O,OH)6 octahedra, alternately one and two octahedra wide, extends along [010]. Chains of edge- and corner-shared Mn(O,OH)6 octahedra coupled by PO4 tetrahedra extend along [010]. By sharing octahedron and tetrahedron corners, these two units form a dense three-dimensional framework, which is further strengthened by weak hydrogen bonding. Chemical analyses by electron microprobe gave a unit formula of (Mn4.99Mg0.02)Σ5.01(P1.76Si0.20As0.07)Σ2.03O8(OH)3.97.P. Elliott and A. Prin