The new Fe2+-rich variety of szaibélyite and its crystal-chemical peculiarities
Zubkova N. V., Pekov I. V., Chukanov N. V., Chaikovskiy I. I., Yapaskurt V. O., Pushcharovsky D. Yu.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2020. V. 149. N 2. P. 72-79
https://doi.org/10.31857/S0869605520020112
Full text is available on eLIBRARY.RU
Language: Russian
Abstract
A new, unusually Fe2+-enriched variety of szaibélyite has been found in the hydrothermal assemblage in the contact zone between kimberlite and a halite rock in the Internatsional’naya kimberlite pipe, Sakha (Yakutia) Republic, Russia. The mineral forms light-green crusts up to 1.5×1.5×0.05 cm inside fractures in ekaterinite aggregates. Its chemical composition (electron microprobe, H2O calculated by stoichiometry) is: MgO 25.52, FeO 28.45, B2O3 36.84, H2O 9.42, total 100.23 wt %; the empirical formula: (Mg1.21Fe2+0.76)Σ1.97B2.02O4(OH)2. The IR spectrum is given and discussed. The crystal structure of the Fe2+-rich szaibélyite variety is solved based on single-crystal XRD data; R = 5.73%. The mineral is monoclinic, P21/c, a = 3.1714(2), b = 10.4561(7), c = 12.6498(9) Å, β = 95.548(7)°, and V = 417.51(5) Å3. Mg and Fe2+ cations are partially ordered between two octahedral sites, the structural formula is: (Fe2+0.51Mg0.49)(Mg0.73Fe2+0.27)(OH)[B2O4(OH)] (Z = 4).
Keywords: szaibélyite, borate mineral, crystal structure, IR spectrum, Internatsional’naya kimberlite pipe
