CRYSTAL CHEMISTRY OF NA-BEARING VESUVIANITE FROM FENITIZED GABBROIDS OF THE WEST KEIVY (KOLA PENINSULA, RUSSIA)
Crystal chemistry of Na-bearing vesuvianite from fenitized gabbroid of the West Keivy (Kola Peninsula, Russia) has been studied by electron microprobe analysis, single crystal X-ray diffraction, infrared spectroscopy and 23Na MAS NMR. The crystal structure has been refined in the P4/nnc space group [a = 15.5141(4), c = 11.7828(5) A, V= 2835.9(2) A3 for sample 976, a = 15.5168(2), c = = 11.7700(4) A, V= 2833.9(1) A3 for sample 50578] to Rt = 0.036, and Rt = 0.041, respectively. Amounts of Na2O in investigated samples 976 and 50578 (wt %) are 0.41 and 0.35, which correspond to 0.63 and 0.54 a.p.f.u. The bands in the IR spectrum are 415, 446, 490, 554, 578, 638, 800, 910, 987, 1020, 3200 (shoulder), 3452, 3564 and 3593 cm b NMR spectrum of sodium consists of asymmetric quadrupolar lineshape doublet at -15.8 ppm, which in magnitude of the chemical shift corresponds to 8-9 coordinated Na. In the crystal structure of vesuvianite sodium is concentrated in the channel sites X1 and X4 mostly in the last of them.