Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) An erratum has been published Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Raade, G. Articles by Balic-Zunic, T. Search for Related Content GeoRef GeoRef Citation

THE CRYSTAL STRUCTURE OF (Be,)(V,Ti)₃O₆, A MINERAL RELATED TO KYZYLKUMITE

Gunnar Raade^1, and Toni Bali-uni²

¹ Department of Geology, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, NO-0318 Oslo, Norway
² Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 København K, Denmark

E-mail address: gunnar.raade{at}nhm.uio.no

The crystal structure of (Be,)(V,Ti)₃O₆, a mineral discovered in the emerald deposit of Byrud, Norway, has been solved and refined to R₁ = 4.51% for 1413 unique reflections. The structure is orthorhombic, Pnma, with lattice parameters a 9.982(1), b 8.502(1), c 4.5480(6) Å, Z = 4, and isotypic with norbergite, Mg₃SiO₄F₂. The empirical chemical formula, based on the electron-microprobe determination of elements heavier than oxygen, and beryllium tentatively calculated to give 1Be for O = 6, is Be(V_1.27³⁺Ti_1.21Cr_0.29Fe_0.08Al_0.07)_2.92O₆. The presence of Be was verified by the structure analysis and a SIMS analysis. The occupancy of the Be site was found to be 0.84(1), which largely explains the surplus of Ti in the empirical formula, as compared to the stoichiometric formula BeV₂TiO₆. However, there is no evidence for ordering of V and Ti on two unique octahedral sites of the structure. The amended empirical formula is (Be_0.840.16)(V_1.32³⁺Ti_1.25Cr_0.29Fe_0.09Al_0.07)_2.02O₆. The appearance of the mineral, the dominance of V and Ti in its composition, and the X-ray powder-diffraction data correspond to those described originally for kyzylkumite, supposed to be V₂Ti₃O₉. The crystal-lattice parameters found earlier for kyzylkumite can be explained as based on an 8 x supercell obtained on a {210} reflection twin. This type of twinning is characteristic for the Byrud mineral, and is present in the crystal used for the structure determination. These facts suggest that the same type of oxide of Be, V and Ti found at Byrud is also the main constituent of material described as kyzylkumite, which probably also contains additional phases, and that a redefinition of this mineral is needed.

Keywords: kyzylkumite, (Be,)(V, Ti)₃O₆, norbergite isotype, leucophoenicite–humite series, crystal structure, twin, V-Ti-Be oxide, Byrud emerald deposit, Norway.