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Refinement of the crystal structure of wöhlerite

Verfeinerung der Kristallstruktur des Wöhlerits

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Summary

The crystal structure of wöhlerite (monoclinicP21,a=10.823(3,b=10.244(3),c=7.290(2) Å, β=109.00(4)o) was refined using 2343 independent diffractions toR 1=0.019 andR 2=0.025.

The refinement confirms the main features of the structure model proposed byShibayeva andBelov (1962), namely the walls of large cation polyhedra interconnected as in cuspidine, with Si2O7 groups linked to the polyhedra. At difference from the structure proposed by the quoted authors, both the Si2O7 groups are clinging to edges of calcium polyhedra.

The cation distribution in the polyhedral walls and the location of fluorine anions are clarified and discussed, resulting in the following crystal chemical formula Na4(Ca7.48Mn0.20Fe0.32)Zr2(Nb1.6Ti0.4) (Si2O7)4O4F2(O1.6F0.4).

Zusammenfassung

Die Kristallstruktur des Wöhlerits (monoklinP21,a 0=10,823(3),b 0=10,244(3),c 0=7,290(2) Å, β=109,00(4)o) wurde mit 2343 unabhängigen Reflexen aufR 1=0,019 undR 2=0,025 verfeinert.

Die Verfeinerung bestätigt im wesentlichen Züge des vonShibayeva undBelov (1962) vorgeschlagenen Strukturmodells, nämlich Bänder aus den Polyedern um die großen Kationen, die — wie im Cuspidin — durch an den Polyedern hängenden Si2O7-Gruppen verknüpft sind.

Die Kationenverteilung in den Polyederbändern und die Lokalisation der Fluor-Anionen wurden aufgeklärt und werden diskutiert; es ergibt sich folgende kristallchemische Formel Na4(Ca7,48 Mn0,20Fe0,32)(Zr2(Nb1,6 Ti0,4) (Si2O7)4O4F2(O1,6F0,4).

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Authors and Affiliations

  1. Istituto di Mineralogia e Petrografia dell', Università di Pisa, via S. Maria 53, I-56100, Pisa, Italy

    M. Mellini &  S. Merlino

  2. C.N.R., Centro di Studio per la Geologia Strutturale e Dinamica dell' Appennino, via S. Maria 53, I-56100, Pisa, Italy

    M. Mellini &  S. Merlino

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  1. M. Mellini
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  2. S. Merlino
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Mellini, M., Merlino, S. Refinement of the crystal structure of wöhlerite. TMPM Tschermaks Petr. Mitt. 26, 109–123 (1979). https://doi.org/10.1007/BF01081296

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