Chabazite-Mg from Gabbroids of the Bazhenovskiy Ophiolite Complex (middle Urals) is the First Find in Russia

The relevance of the work is due to the need to study a large and diverse group of zeolites, chabazite-Mg, in particular, it’s an extremely rare member of that group. This mineral was discovered in 2010 in the basalts of Hungary, and our discovery is second in the world and first one in Russia. The purpose of the work: a comprehensive study of chabazite-Mg from gabbroids of the Bazhenovskiy ophiolite complex (Middle Urals). Methodology of research: The chemical composition of the zeolite is determined using a JSM-6390LV scanning electron microscope by Jeol with the INCA Energy 450 X-Max 80 energy dispersive device by Oxford Instruments (Ural Branch of the Russian Academy of Sciences, Ekaterinburg). We chose the faces of the crystals with a flat surface and perpendicular to the analyzer. The obtained quantitative analyzes are recalculated taking into account the predicted water content in the mineral. X-ray diffraction study of the zeolite was carried out with an XRD-7000 X-ray diffractometer by Shimadzu (Ural Branch of the Russian Academy of Sciences, Ekaterinburg). Conditions for survey of zeolite: copper radiation, V = 40 kV, I = 30 mA, step size – 0.02. Results. In late ruptures in association with calcite, pyrite, and laumontite, clay-like material contains water-transparent cuboid crystals with a size of up to 0.2 mm, as well as their crustaceous segregation with a size of up to 2–3 mm. The crystals are composed of rhombohedron r {1011}, as well as the typical chabazite twins intergrowth with twining axis [0001]. A diffractometric study of the selected crystals showed that they were represented by zeolite from chabazite group. The main reflections of zeolite (in Å) are 9.29; 6.88; 5.53; 4.96; 4.31; 3.85; 3.55; 3.44; 2.922; 2.868, etc. The unit cell dimensions calculated on the basis of the X-ray diffraction pattern in the hexagonal positioning are the following (in Å) – aH = 13.73 (4); cH = 14.83 (4); V = 2437.45 (5). The chemical assemblage of the mineral is fairly uniform and quite confidently recalculated for chabazite-Mg. The average crystalchemical formula of the mineral is (Mg0.82Ca0.71K0.09) 1.62 [(Al2.99Fe0.06Si8.95) 12.00O24]10 H2 O (based on 24 oxygen atoms). In Bazhenovskiy chabazite-Mg, a high Si / (Si + Al) ratio is about 0.75, which is generally characteristic of a given zeolite (0.74 in reference). Conclusion. We have determined chabazite-Mg in the gabbroids of the Bazhenovskiy ophiolite complex. The discovery of this mineral is associated with later carbonate-sulphide veinlets, i.e., chabazite-Mg captures the final stage of development of zeolites in gabbroids. This fact expands our knowledge of the zeolite mineralization of the Bazhenovskiy ophiolite complex. It is noteworthy that zeolite was found not in basalts, but in ophiolite gabbroids.