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Kyzylkumite: a finding in the southern Baikal region, Russia and refinement of its crystal chemical formula |
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| Authors: | L Z Reznitsky E V Sklyarov T Armbruster L F Suvorova Z F Uschapovskaya S V Kanakin |
| Institution: | 1. Institute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia 2. University of Bern, Friestrasse 3, CH-3012, Bern, Switzerland 3. Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, ul. Favorskogo 1A, Irkutsk, 664033, Russia 4. Geological Institute, Siberian Branch, Russian Academy of Sciences, ul. Sakh’yanovoi 6, Ulan-Ude, 670042, Russia |
| Abstract: | Kyzylkumite has been found in Cr-V-bearing metamorphic rocks of the Sludyanka Complex, Southern Baikal region; it has been identified by X-ray powder diffraction method. This is a late secondary mineral developed after Ti-V-oxides (schreyerite, berdesinskiite) and V-bearing rutile and titanite. Kyzylkumite represents a new structural type with composition Ti4V 2 3+ O10(OH)2 corresponding to octahedral coordination of Ti4+ and V3+. Its unit-cell dimensions are: a = 8.4787(1), b = 4.5624(1), c = 10.0330(1) Å, β = 93.174(1)°. The ideal formula of kyzylkumite Ti4V 2 3+ O10(OH)2 corresponds to composition, wt %: 65.56 TiO2, 30.75 V2O3, 3.69 H2O. Indeed, the contents (wt %) of these constituents range from 62 to 70 TiO2 and from 23 to 33 V2O3. Variations in contents and the Ti/V value are caused by partial substitution V3+ for V4+, isovalent substitutions Ti4+ and V3+ for V4+ and Cr3+, respectively, and coupled substitution V3+ + OH? ? Ti4+ + O2?. Smyslova et al. (1981)—the discovereres of kyzylkumite—assumed its composition to be the same as for schreyerite V 2 3+ Ti3O9 that principally different from kyzylkumite from the Sludyanka Complex. Therefore, re-examination of the kyzylkumite holotype or cotype from its type locality is needed. |
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