Ab initio X-ray powder structure determination of parascorodite, Fe(H₂O)₂AsO₄

Authors: Perchiazzi, Natale; Ondruš, Petr; Skála, Roman

Source: European Journal of Mineralogy, Volume 16, Number 6, 2004 , pp. 1003-1007(5)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

The crystal structure of parascorodite, Fe(H₂O)₂AsO₄, has been solved ab-initio from powder data. The mineral is trigonal, with space group P3c1, Z = 6, a = 8.9232(2) Å, c = 9.9296 (3) Å. The Rietveld refinement was led up to R_p = 4.5 %. The structure is built up by the same coordination polyhedra found in its dimorph scorodite, namely slightly distorted Fe-centred octahedra and Ascentred tetrahedra, but their connection lead to quite different crystal structures for the two polymorphs. Parascorodite structure can be described in terms of mixed octahedral-tetrahedral "columns" including Fe2 and As polyhedra, running along c, similar to those found in ferrinatrite and kaatialaite. These columns are interconnected in a threedimensional framework by the sharing of the O1 oxygen between [AsO₄] tetrahedra and Fe1 octahedra, and by the strong hydrogen bond OW···O2.

Keywords: PARASCORODITE; KANK; POWDER DATA; AB-INITIO; STRUCTURAL SOLUTION

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0935-1221/2004/0016-1003

Publication date: 2004-01-01

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