Crystal chemistry of neptunite from the Khan Bogdo alkaline massif (Mongolia)

A. A. Zolotarev, N. V. Vladykin, S. V. Krivovichev, T. L. Panikorovskii

Research output

Abstract

Crystal chemical characteristics have been studied for neptunite from alkaline granites of the Khan Bogdo massif (Southern Mongolia). The mineral occurs to be the practically clear Fe-variety of its species. Refinement of its crystal structure was carried out in two space groups: centric C2/c and acentric Cc. It is indicated that correct space group is the acentric Cc due to ordering of octahedral cations Ti and Fe. The structure was refined to R 1 = 0.025 (wR 2 = 0.057) for 4889 reflections with |Fo| ≥ 4σF. Unit cell parameters: a = 16.4542(7), b = 12.5115(4), c = 9.9980(4) Å, β = 115.542(5)°, V = 1857.10(15) Å 3 , Z = 4. Ti octahedra show strong distortions: one bond Ti-O 1.75 Å, another bond 2.20 Å, and four Ti-O bonds around 2.0 Å. Fe octahedra have a more regular shape with an average bond length Fe-O 2.13-2.14 Å. Empirical formula calculated on the basis of chemical analysis is (K 0.86 Cs 0.02 Zn 0.02 Ca 0.01 ) S0.91 Na 1.90 Li 0.82 (Fe 1.54 2+ Fe 0.22 3+ Mn 0.16 Mn 0.04 ) S1.96 Ti 2.1 (Si 7.76 Al 0.25 )O 24 . Structural formula is K 0.97 Na 1.90 (Li 0.94 Na 0.06 ) S1.00 (Fe 1.80 Mn 0.15 Mg 0.05 ) S2.00 Ti 2 Si 8 O 22 (O,OH) 2 . Idealized formula is KNa 2 LiFe 2 Ti 2 Si 8 O 24

Original languageEnglish
Pages (from-to)112-127
Number of pages16
JournalZapiski Rossiiskogo Mineralogicheskogo Obshchestva
Volume145
Issue number2
Publication statusPublished - 1 Jan 2016

Scopus subject areas

  • Geochemistry and Petrology
  • Geology
  • Economic Geology
  • Materials Chemistry

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