The crystal structure of joosteite, (Mn2+,Mn3+,Fe3+)2[PO4]O, from the Helikon II Mine, Karibib (Namibia), and its relationship to staneekite, (Fe3+,Mn2+,Fe2+,Mg)2[PO4]O (original) (raw)

Original paper

Keller, Paul; Lissner, Falk; Schleid, Thomas

Abstract

The crystal structure of joosteite, (Mn2+,Mn3+,Fe3+)2[PO4]O, from the type locality Helikon II pegmatite, Karibib (Namibia), space group I2/a, a 11.888(2), b 6.409(1), c 9.804(2) Å, ß 106.17(3)°, Z = 8, was determined from single-crystal X-ray diffraction intensity data and refined up to R1 = 0.0414, R1<4σ = 0.0373, and wR2 = 0.0958. Joosteite is isostructural with staněkite-Mabc, (Fe3+,Mn2+,Fe2+,Mg)2[PO4]O. The crystal structure consists of a distorted [PO4] tetrahedron and two symmetrically different, strongly distorted [MO6] octahedra. Similar to staněkite-Mabc, the cations M2+ and M3+ (M = Mn and Fe) are distributed over both octahedral sites. The [MO6] octahedra share common edges to form zigzag chains running parallel to [010] for [(M1)O6] and to [100] for [(M2)O6], respectively. Both chain types are further interconnected by additional edges along the c axis to build an open framework that hosts the [PO4] tetrahedra. Synthetic polymorphs of joosteite or pure Mn2[PO4]O are unknown in contrast to staněkite-Mabc, where α-Fe2[PO4]O is characterized by face-sharing [MO6] octahedra joined together by common vertices to form tightly folded zigzag chains and β-Fe2[PO4]O-I or β-Fe2[PO4]O-II is likewise joined together by common vertices but forms straight chains. Joosteite is possibly of interest for the Li-battery technology and catalytic properties could be expected.

Keywords

joosteite • (mn2+ • mn3+ • fe3+)2[po4]o • crystal structure • stanekite • polymorphism • pegmatite • namibia