Byzantievite, Ba-5(Ca,REE,Y)(22)(Ti,Nb)(18)(SiO4)(4)[(PO4),(SiO4)](4) (BO3)(9)O-21[(OH),F](43)(H2O)(1.5): the crystal structure and crystal chemistry of the only known mineral with the oxyanions (BO3), (SiO4) and (PO4)

作者：Sokolova E^*; Hawthorne F C; Pautov L A; Agakhanov A A

来源：Mineralogical Magazine, 2010, 74(2): 285-308.

DOI：10.1180/minmag.2010.074.2.285

• byzantievite
• new mineral
• borate-silicate-phosphate
• electron microprobe analysis
• crystal structure
• short-range order
• Dara-i-Pioz massif
• Tajikistan

The crystal structure of byzantievite, Ba-5(Ca,REE,Y)(22)(Ti,Nb)(18)(SiO4)(4)[(PO4),(SiO4)](4)(BO3)(9)O-21[(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 R-1 = 13.14% based on 3794 observed [F-o >4 sigma vertical bar F vertical bar] unique reflections measured with Mo-K alpha X-radiation on a Bruker P4 diffractometer equipped with a CCD detector. Byzantievite is hexagonal, space group R3, a = 9.1202(2) angstrom, c = 102.145(5) angstrom, V = 7358.0(5) angstrom(3), Z = 3, D-calc = 4.151 g cm(-3). The empirical formula (electron microprobe analysis) is Ba-5.05[(Ca8.99Sr0.96Fe0.422+Na0.20)(Sigma 10.57)(Ce3.46La1.54Nd1.20Pr0.30Sm0.26Dy0.41Gd0.32Th0.39U0.174+)(Sigma 8.05)Y-3.53](Sigma 22.15)(Ti12.31Nb5.30)(Sigma 17.61)(SiO4)(4.65)(PO4)(3.12)(BO3)(8.89)O-22.16(OH)(38.21)F-4.89(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.

• 出版日期2010-4