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: (Mg_1.21Fe²⁺_0.76)_Σ1.97B_2.02O₄(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) ų. Mg and Fe²⁺ cations are partially ordered between two octahedral sites, the structural formula is: (Fe²⁺_0.51Mg_0.49)(Mg_0.73Fe²⁺_0.27)(OH)[B₂O₄(OH)] (Z = 4).

Keywords: szaibélyite, borate mineral, crystal structure, IR spectrum, Internatsional’naya kimberlite pipe