Unique thallium mineralization in the fumaroles of the Tolbachik volcano, Kamchatka Peninsula, Russia. II. Karpovite, Tl₂VO(SO₄)₂(H₂O)

Author： Siidra Oleg I. Vergasova Lidiya P. Kretser Yuri L. Polekhovsky Yuri S. Filatov Stanislav K. Krivovichev Sergey V.

Publisher： Mineralogical Society

E-ISSN： 1471-8022|78|7|1699-1709

ISSN： 0026-461X

Source： Mineralogical Magazine, Vol.78, Iss.7, 2014-12, pp. : 1699-1709

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Abstract

Karpovite, ideally Tl₂VO(SO₄)₂(H₂O), was found in a fumarole of the 1st cinder cone of the North Breach of the Great Fissure Tolbachik volcano eruption (1975–1976), Kamchatka Peninsula, Russia. Karpovite occurs as bundles of white, needle-like crystals associated with shcherbinaite, pauflerite, bobjonesite, markhininite, evdokimovite and microcrystalline Mg, Al, Fe and Na sulfates. Karpovite is monoclinic, P2₁, a = 4.6524(4), b = 11.0757(9), c = 9.3876(7) Å, β = 98.353(2)°, V = 478.60(7) Å³, Z = 2 (from single-crystal diffraction data). The eight strongest lines of the X-ray powder diffraction pattern are (I/d/hkl): 64/4.289/012, 81/4.253/110, 38/3.683/111, 47/3.557/022, 100/3.438/1¯21, 52/2.982/013, 59/2.945/112, 54/2.354/132. The chemical composition determined by the electron microprobe analysis is (wt.%) Tl₂O 61.43, VO₂ 11.53, SO₃ 23.55, H₂O 2.61, total 99.12. The empirical formula (calculated on the basis of 10 O a.p.f.u.) is Tl_2.00V_0.96S_2.03O₉(H₂O). The simplified formula of karpovite is Tl₂VO(SO₄)₂(H₂O), which requires Tl₂O 61.93, VO₂ 12.09, SO₃ 23.34, H₂O 2.62 total 100.00 wt.%. The crystal structure was solved by direct methods and refined to R₁ = 0.026 for 4196 independent observed reflections. The structure contains two symmetrically independent Tl⁺ sites, one V⁴⁺ site and two S⁶⁺ sites. VO₅H₂O octahedra and SO₄ tetrahedra link together by sharing corners to form kröhnkite-type stripes parallel to the a axis with their planes oriented parallel to (021) and (021). Tl⁺ cations are located between the chains, linked into a three-dimensional structure. The new mineral is named in honour of Professor Gennadii Alexandrovich Karpov (b. 1938), volcanologist at the Institute of Volcanology, Russian Academy of Sciences, Petropavlovsk-Kamchatskii, Kamchatka Peninsula, Russia.