From structure topology to chemical composition. X. Titanium silicates: the crystal structure and crystal chemistry of nechelyustovite, a group III Ti-disilicate mineral

摘要

The crystal structure of nechelvustovite, ideally Na_4Ba_2Mn_(1.5) square _(2.5)Ti_5Nb(Si_2O_7)_4O_4(OH0_3F(H_2O)_6, a 5.447(1) A, b 7.157(1) A, c 47.259(9) A, alpha 95.759(4)°, beta 92.136(4)°, gamma 89.978(4)°, V 1831.7(4) A~3, space group P1,Z=2, D_(calc). 3.041 g cm~(-3), from Lovozero alkaline massif, Kola Peninsula, Russia, has been solved and refined to R_1 = 13.9% on the basis of 1745 unique reflections (F_o > 15 sigma F). Electron microprobe analysis yielded the empirical formula (Na_(4.21)Mn_(1.11)~(2+)Ca_(0.46) square _(1.22))_(SIGMA 7.00) (Ba_(1.28)Sr_(0.50)K_(0.30) square _(0.92))_(SIMGA 3.00) (Ti_(4.14)Nb_(1.43)Mn_(0.33)~(2+)Fe_(0.06)~(3+)Al_(0.04))_(SIGMA6.00)(sI_(8.03)O_(28))O_(3.99)[OH)_(2.94)F_(1.06)]_(SIGMA 4.00) (H_2O)_(6.01), Z = 2, calculated on the basis of 42 (O + F) a.p.f.u., H_2O and OH are calculated from structure refinement (H_2O = 6 p.f.u.; F + OH = 4 p.f.u.). The crystal structure of nechelyustovite is a combination of a TS (titanium silicate) block and an I (intermediate) block.