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Byzantievite, Ba5(Ca,REE,Y)22(Ti,Nb)18(SiO4)4[(PO4),(SiO4)]4 (BO3)9O21[(OH),F]43(H2O)1.5: the crystal structure and crystal chemistry of the only known mineral with the oxyanions (BO3), (SiO4) and (PO4)

Published online by Cambridge University Press:  05 July 2018

E. Sokolova ,
F. C. Hawthorne ,
L. A. Pautov  and
A. A. Agakhanov
E. Sokolova*
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2 Canada Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Moscow, 119017 Russia
F. C. Hawthorne
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2 Canada
L. A. Pautov
Affiliation:
Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow 117071 Russia
A. A. Agakhanov
Affiliation:
Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow 117071 Russia
*
*E-mail: [email protected]
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Abstract

The crystal structure of byzantievite, Ba5(Ca,REE,Y)22(Ti,Nb)18(SiO4)4[(PO4),(SiO4)]4 (BO3)9O21[(OH),F]43(H2O)1.5, a new mineral from the moraine of the Dara-i-Pioz glacier, the Alai mountain ridge, Tien-Shan Mountains, northern Tajikistan, was solved by direct methods and refined to R1 = 13.14% based on 3794 observed [Fo >4σ|F|] unique reflections measured with Mo-Kα X-radiation on a Bruker P4 diffractometer equipped with a CCD detector. Byzantievite is hexagonal, space group R3, a = 9.1202(2) Å, c = 102.145(5) Å, V = 7358.0(5) Å3, Z = 3, Dcalc. = 4.151 g cm–3. The empirical formula (electron microprobe analysis) is Ba5.05[(Ca8.99Sr0.96Fe2+0.42Na0.20)Σ10.57(Ce3.46La1.54Nd1.20Pr0.30Sm0.26Dy0.41Gd0.32Th0.39U4+0.17)Σ8.05Y3.53]Σ22.15(Ti12.31Nb5.30)Σ17.61(SiO4)4.65(PO4)3.12(BO3)8.89O22.16(OH)38.21F4.89(H2O)1.5, Z = 3, calculated on the basis of 124.5 (O + F) a.p.f.u. The H2O and OH contents were calculated from structure refinement (F + OH = 43 a.p.f.u.; H2O = 1.5 a.p.f.u..), and B was determined by SIMS. The crystal structure is a framework of Ti-Ba-Ca-REE-dominant polyhedra and SiO4, PO4 and BO3 groups. In the crystal structure, there are 50 cation sites, 23 of which are fully occupied and 27 partly occupied: six of the 27 partly-occupied sites are >50% occupied, 21 <50% occupied. The crystal structure of byzantievite is an intercalation of three components, one fully ordered with 100% occupancy of cation sites, and two partly ordered with cation-site occupancies of 67% and 17% respectively. Byzantievite is the only known mineral that contains all three of the oxyanions (BO3), (SiO4) and (PO4) as essential components.

Keywords

byzantievitenew mineralborate-silicate-phosphateelectron microprobe analysiscrystal structureshort-range orderDara-i-Pioz massifTajikistan
Type
Research Article
Information
Mineralogical Magazine , Volume 74 , Issue 2 , April 2010 , pp. 285 - 308
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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