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Natromolybdite, Na2MoO4·2H2O, a new mineral from fumarole deposits of the Tolbachik volcano, Kamchatka, Russia

Published online by Cambridge University Press:  24 June 2025

Igor V. Pekov ,
Sergey N. Britvin Open the ORCID record for Sergey N. Britvin [Opens in a new window] ,
Natalia N. Koshlyakova Open the ORCID record for Natalia N. Koshlyakova [Opens in a new window] ,
Atali A. Agakhanov ,
Dmitry I. Belakovskiy ,
Nikita V. Chukanov ,
Dmitry A. Ksenofontov ,
Anna G. Turchkova  and
Pavel S. Zhegunov Open the ORCID record for Pavel S. Zhegunov [Opens in a new window]
Igor V. Pekov*
Affiliation:
Faculty of Geology, Moscow State University, Moscow, Russia
Sergey N. Britvin
Affiliation:
Saint Petersburg State University, Saint Petersburg, Russia
Natalia N. Koshlyakova
Affiliation:
Faculty of Geology, Moscow State University, Moscow, Russia
Atali A. Agakhanov
Affiliation:
Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia
Dmitry I. Belakovskiy
Affiliation:
Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia
Nikita V. Chukanov
Affiliation:
Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry, Russian Academy of Sciences, Chernogolovka, Moscow region, Russia
Dmitry A. Ksenofontov
Affiliation:
Faculty of Geology, Moscow State University, Moscow, Russia
Anna G. Turchkova
Affiliation:
Faculty of Geology, Moscow State University, Moscow, Russia
Pavel S. Zhegunov
Affiliation:
Institute of Volcanology and Seismology, Far Eastern Branch of Russian Academy of Sciences, Petropavlovsk-Kamchatsky, Russia
*
Corresponding author: Igor V. Pekov; Email: igorpekov@mail.ru
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Abstract

The new mineral natromolybdite, ideally Na2MoO4·2H2O, was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. The associated minerals are halite, sylvite, aphthitalite, belomarinaite, powellite, hematite, sanidine, tilasite, johillerite, bradaczekite, badalovite, arsmirandite, wrightite, arsenatrotitanite, dmisokolovite, litidionite, rutile and cristobalite. Natromolybdite occurs as rectangular, octagonal or rhomb-like lamellar to thin-tabular crystals up to 40 μm across and up to 3 μm thick, in near-parallel, pile-like or rose-like aggregates and crystal crusts up to 0.2 mm across. It is transparent and colourless, with vitreous lustre. Dcalc is 2.573 g/cm3. The synthetic analogue of natromolybdite is optically biaxial (+), α = 1.575(2), β = 1.576(2), γ = 1.598(3) and 2Vmeas = 20(10)°. The chemical composition (wt.%, electron microprobe, H2O is calculated by stoichiometry) is: Na2O 25.51, K2O 0.66, SO3 1.04, MoO3 58.21, H2Ocalc 15.05, total 100.47. The empirical formula, calculated based on O = 6 apfu, is (Na1.971K0.034)Σ2.005(Mo0.968S0.031)Σ0.999O4·2H2O. Natromolybdite is orthorhombic, space group Pbca, a = 8.483(1), b = 10.577(2), c = 13.842(2) Å, V = 1242.0(2) Å3 and Z = 8. The nine strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 6.92(100)(002), 4.243(20)(200), 4.206(32)(022), 3.618(31)(202), 3.310(31)(220), 3.169(49)(131), 3.067(21)(114), 2.987(30)(222) and 2.681(15)(204, 311). Natromolybdite (IMA-accepted symbol Nmyb) is named for the chemical composition. It is a natural analogue of a well-studied synthetic sodium molybdate dihydrate.

Keywords

natromolybditenew mineralsodium molybdate dihydratefumarole sublimateTolbachik volcano

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Type
Article
Information
Mineralogical Magazine , First View , pp. 1 - 6
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of The Mineralogical Society of the United Kingdom and Ireland.

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Footnotes

Associate Editor: Daniel Atencio

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