New data on mineralogy and crystal chemistry of the lovozerite group: unusual varieties of kazakovite and litvinskite

Zubkova N. V., Pekov I. V., Chukanov N. V., Grishin V. G., Koshlyakova N. N., Yapaskurt V. O., Ksenofontov D. A., Turchkova A. G., Pushcharovsky D. Yu.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2021. V. 150. N 5. P. 134-152

https://doi.org/10.31857/S0869605521040109

Language: Russian

Abstract

Unusual chemical and structural varieties of two lovozerite-group minerals from the Lovozero alkaline complex (Kola Peninsula) were studied by means of electron microprobe analysis, single-crystal X-ray diffraction and IR spectroscopy. A Zr- and Fe-enriched variety of kazakovite with the composition Na_6.20U_0.01(H₃O)_0.25(Mn_0.72Ca_0.10)_Σ0.82(Ti_0.61Zr_0.18 Fe³⁺_0,18)_Σ0.97Si_6O17.83(OH)_0.17 was found in the Palitra pegmatite at Mt. Kedykverpakhk. The mineral is trigonal, R-3m, a = 10.2622(5), с = 13.0884(7) Å, V = 1193.71(13) Å3; R_hkl = 0.0383. The variety of trigonal litvinskite from Mt. Alluaiv is characterized by the lowest content of large cations sum (Na,Ca and Mn) and previously unknown for this mineral species space group R3m. Its composition is Na_2.05(H₂O)_0.64(Mn_0.13Ca_0.02)_Σ0.15(Zr_0.93Ti_0.06 )_Σ1.01Si₆O_12.36(OH)_5.64, and unitcell parameters are: a = 10.1880(10), с = 13.1209(16) Å, V = 1179.4(3) Å3; R_hkl = 0.0665. Thepresence of hydronium H₃O+ was first found for lovozerite-group minerals. The way of formation of kapustinite and litvinskite as a result of the step-by-step townendite alteration process (decationization with the replacing of the corresponding part of O^2– by OH^–) is discussed.

Keywords: lovozerite group, kazakovite, litvinskite, crystal structure, zeolite-like silicate with heteropolyhedral framework, microporous material, hyperagpaitic pegmatite, Lovozero alkaline complex, Kola Peninsula