Description and crystal structure of nabiasite, BaMn9[(V,As)O4]6(OH)2, a new mineral from the Central Pyrenees (France)

Joël Brugger, Michel Bonin, Kurt J. Schenk, Nicolas Meisser, Peter Berlepsch, Alain Ragu

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11 Citations (Scopus)

Abstract

Nabiasite, ideally BaMn9[(V,As)O4]6(OH)2, is a new mineral which occurs in rhodochrosite-, friedelite- and barite-bearing veinlets crosscutting Mn ores at the historic Pla de Labasse deposit near the Nabias hamlet, Central Pyrenees, France. These syn-genetic exhalative ores are embedded in Lower Carboniferous Radiolarian cherts and have acquired a complex mineralogy during the Hercynian metamorphism which culminated under upper-greenschist-facies conditions. The fresh metamorphosed ores consist of rhodonite, rhodochrosite, friedelite, tephroite, spessartine, braunite, hausmannite, locally abundant tinzenite and pyroxmangite, ± fluorapatite, strontian barite, hyalophane, rutile, and pyrophanite. Ba and V (± As) have probably been enriched together with Mn by syn-genetic processes. Thus, nabiasite is a product of the hydrothermal remobilization of syn-genetic concentrations, possibly by fluids originating from late Hercynian granitic intrusions. Nabiasite is a rare mineral occurring as red anhedral grains up to 100 μm in diameter. It is cubic with a = 12.832(2) Å and space group Pa 3, Z = 4. Its structure has been determined and refined to R1 = 0.0263 for 854 unique reflections with I > 2σ(I), collected on a Stoe IPDS using MoKα X-radiation. The structure of nabiasite contains two symmetry-independent Mn2+ octahedrally coordinated by O, one Mn2+ in octahedral coordination with five O and one OH group, one V5+ in tetrahedral coordination with O, and one Ba2+ in twelve-fold coordination with O. The structure is based on a cubic close-packed anionic framework, with close-packed planes parallel to (111). One of every nine close-packed positions in the plane passing through the origin is occupied by a Ba atom instead of a O atom. The structure of nabiasite can be described as a three-dimensional framework of edge-sharing MnO6-octahedra, with cavities which host Ba(VO4)6 groups.

Original languageEnglish
Pages (from-to)879-890
Number of pages12
JournalEuropean Journal of Mineralogy
Volume11
Issue number5
DOIs
Publication statusPublished - 1 Jan 1999

Keywords

  • Crystal structure
  • Manganese deposit
  • Nabiasite
  • New mineral
  • Vanadate

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