Bobtraillite from Gejiu hyperagpaitic nepheline syenite, southwestern China: new occurrence and crystal structure

Abstract. A second occurrence of bobtraillite is described from the Gejiu nepheline syenite, southwestern China. The extremely rare and complex boron-bearing zirconium silicate associated with albite, orthoclase, jadeite, fluorite, andradite, titanite, as well other REE zirconium-bearing minerals, catapleiite, moxuanxueite, låvenite, eudialyte, britholite-(Ce), calcioancylite-(La). EMP LA-ICP-MS analyses studied material give an empirical formula: (Na9.70Li0.42K0.08□1.80)Σ12.00(Sr10.61Ca1.14Fe0.07□0.18)Σ12.00(Zr12.87Ti0.53Nb0.31REE0.08Y0.06U0.02Th0.01□0.12)Σ14.00(Si42.41B5.59Al0.02)Σ48.02O132(OH)12 ⚫ 12H2O. Bobtraillite trigonal, space group P3¯c1, a=19.6977(6), c=9.9770(3) Å, V=3352.4(2) Å3, Z=1. Single-crystal structure refinement revealed that all sodium occupies Na(1) Na(2) sites; site occupancy these two positions 0.835(18) 0.15(2), respectively, suggesting Na dominant, while a vacancy-dominant site. [8]-coordinated has been assigned to Sr Ca, free factors, 0.874(10) 0.126(10), respectively. These new data indicate ideal formula could be written (Na,□)12(□,Na)12Sr12Zr14(Si3O9)10[Si2BO7(OH)2]6