Pyrosmalite-(Fe), Fe 8Si 6O 15(OH,Cl) 10

Hexiong Yang, Robert T Downs, Yongbo W. Yang, Warren H. Allen

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Abstract

Pyrosmalite-(Fe), ideally Fe II 8Si 6O 15(OH,Cl) 10 [refined composition in this study: Fe 8Si 6O 15(OH 0.814Cl 0.186) 10·-0.45H 2O, octairon(II) hexasilicate deca(chloride/hydroxide) 0.45-hydrate], is a phyllosilicate mineral and a member of the pyrosmalite series (Fe,Mn) 8Si 6O 15(OH,Cl) 10, which includes pyrosmalite-(Mn), as well as friedelite and mcgillite, two polytypes of pyrosmalite-(Mn). This study presents the first structure determination of pyrosmalite-(Fe) based on singlecrystal X-ray diffraction data from a natural sample from Burguillos del Cerro, Badajos, Spain. Pyrosmalite-(Fe) is isotypic with pyrosmalite-(Mn) and its structure is characterized by a stacking of brucite-type layers of FeO 6-octahedra alternating with sheets of SiO 4 tetrahedra along [001]. These sheets consist of 12-, six-and four-membered rings of tetrahedra in a 1:2:3 ratio. In contrast to previous studies on pyrosmalite-(Mn), which all assumed that Cl and one of the four OH-groups occupy the same site, our data on pyrosmalite-(Fe) revealed a split-site structure model with Cl and OH occupying distinct sites. Furthermore, our study appears to suggest the presence of disordered structural water in pyrosmalite-(Fe), consistent with infrared spectroscopic data measured from the same sample. Weak hydrogen bonding between the ordered OH-groups that are part of the brucitetype layers and the terminal silicate O atoms is present.

Original languageEnglish (US)
JournalActa Crystallographica Section E: Structure Reports Online
Volume68
Issue number1
DOIs
Publication statusPublished - Jan 2012

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Keywords

  • Data-to-parameter ratio = 16.4
  • Disorder in main residue
  • H-atom completeness 83%
  • Mean σ(Fe-O) = 0.001 Å
  • R factor = 0.023
  • Single-crystal X-ray study
  • T = 293 K
  • wR factor = 0.068

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Materials Science(all)
  • Chemistry(all)

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