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

Authors: Keller, Paul; Lissner, Falk; Schleid, Thomas

Source: Neues Jahrbuch für Mineralogie - Abhandlungen, Volume 184, Number 2, October 2007 , pp. 225-230(6)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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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, R_1<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

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0077-7757/2007/0095

Publication date: 2007-10-01

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