Mineralogy and Petrology

, Volume 38, Issue 3, pp 201–211 | Cite as

Sigioite : The oxidation mechanism in [M 2 3 + (PO4)2(OH)2(H2O)2]2 - structures

  • Frank C. Hawthorne
Article
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Summary

The crystal structure of sigloite, Fe3 [(H2O)3OH] [Al2(PO4)2(OH)2(H2O)2]- 2 H2O, triclinic, a 5.190 (2), b 10.419 (4), c 7.033 (3) Å, α 105.00 (3), β 111.31(3), γ 70.87 (3)°, V 330.5 (2) Å3, Z = 1, space group P\(\bar 1\), has been refined to anR index of 5.3% using 1713 observed (I > 2.5 σ 1) reflections collected with graphite-monochromated MoKα X-rays. Sigloite is isostructural with the laueite-group minerals. Corner-linked [A1□5] chains (□: unspecified ligand) are cross-linked by (PO4) tetrahedra to form a mixed corner-linked tetrahedral-octahedral sheet of composition [A12(PO4)2(OH)2(H2O)2]2-. These sheets are linked by (Fe3+O2(OH, H2O)4) octahedra and two (H2O) groups that participate in a hydrogen-bonding network. Sigloite is the oxidized equivalent of paravauxite, Fe2+(H2O)4[Al2(PO4)2(OH)2(H2O)2]-2 H2O, and detailed comparison of the two structures shows that the oxidation mechanism involves loss of hydrogen from one of the (H2O) groups coordinating the Fe3+, and positional disorder of both the Fe3+ and (OH) and (H2O) ligands.

Keywords

Oxidation Hydrogen Reflection Crystal Structure Geochemistry 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Siggloit: Der Oxidationsmechanismus in (M 2 3 + (PO4)2(OH)2(H2O)2]2- Strukturen

Zusammenfassung

Die Kristallstruktur von Sigloit, Fe3+ [(H2O)3OH] [Al2(PO4)2(OH)2(H2O)2].2 H2O, triklin, a 5,190 (2), b 10,419 (4), c 7,033 (3) Å, α 105,00 (3), β 111,31 (3), γ 70,87 (3)°, V 330,5 (2) Å3,Z = 1, Raumgruppe P\(\bar 1\), wurdefür 1713 beobachtete Reflexe (I > 2,5 σ I), die mit MoKa-Röntgenstrahlung (Graphit-Monochromator) gesammelt wurden, auf einen R-Wert von 5,3% verfeinert. Sigloit ist isotyp mit den Mineralen deer Laueit-Gruppe. Über Ecken verknüpfte [A1□5]-Ketten (□: nicht spezifizierter Ligand) werden über (P04)-Tetraeder zu ebenfalls über Ecken verknüpfte Tetraeder-OktaederSchichten der Zusammensetzung [A12(PO4)2(OH)2(H2O)2]2- verbunden. Diese Schichten werden über (Fe3+O2(OH, H2O)4)-Oktaeder und zwei (H2O)-Gruppen, die am

Wasserstoffbrücken-Netzwerk beteiligt sind, verbunden. Sigloit ist das oxidierte Analogon zu Paravauxit, Fe2+(H2O)4[A12(PO4)2(OH)2(H2O)2] - 2 H2O; ein detaillierter Vergleich dieser beiden Strukturen zeigt, daß der Oxidationsmechanismus sowohl den Verlust eines Wasserstoffatoms (H2O)-Gruppe, welche ein Fe3+-Atom koordiniert, als auch eine Fehlordnung der Punktlagen von Fe3+ und von den (OH) und (H2O) Liganden bedingt.

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References

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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Frank C. Hawthorne
    • 1
  1. 1.Department of Geological SciencesUniversity of ManitobaManitobaCanada

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