• Avdontseva, Evgenia Yu.
• Kargopoltsev, Anatoly A.
• Avdontceva, Margarita S.
• Shorets, Olga
• Moskaleva, Svetlana V.
• Vergasova, Lidiya P.
• Filatov, Stanislav
• Shablinskii, Andrey

Abstract

<jats:title>Abstract</jats:title><jats:p>Medvedevite, KMn<jats:sup>2+</jats:sup>V<jats:sup>5+</jats:sup><jats:sub>2</jats:sub>O<jats:sub>6</jats:sub>Cl⋅2H<jats:sub>2</jats:sub>O, is a new mineral discovered in the Toludskoe lava field, formed during the 2012–2013 Tolbachik fissure eruption. The mineral occurs as thin acicular transparent bright red crystals up to 0.15 mm. Medvedevite is associated with thénardite, halite, aphthitalite, leonite, kieserite, eugsterite and syngenite. The empirical formula calculated on the basis of 13+ positive charge units for the anhydrous part and 2H<jats:sub>2</jats:sub>O is (K<jats:sub>1.02</jats:sub>Na<jats:sub>0.03</jats:sub>)<jats:sub>Σ1.05</jats:sub>Mn<jats:sup>2+</jats:sup><jats:sub>0.95</jats:sub>(V<jats:sup>5+</jats:sup><jats:sub>1.92</jats:sub>S<jats:sup>6+</jats:sup><jats:sub>0.05</jats:sub>Si<jats:sub>0.04</jats:sub>)<jats:sub>Σ2.01</jats:sub>O<jats:sub>6.02</jats:sub>Cl<jats:sub>0.96</jats:sub>⋅2H<jats:sub>2</jats:sub>O. The crystal structure of medvedevite was determined using single-crystal X-ray diffraction data: monoclinic crystal system, the space group is <jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>c</jats:italic>, <jats:italic>a</jats:italic> = 7.1863(2), <jats:italic>b</jats:italic> = 10.1147(3), <jats:italic>c</jats:italic> = 12.7252(4) Å, β = 106.243(3)°, <jats:italic>V</jats:italic> = 888.04(5) Å<jats:sup>3</jats:sup>, <jats:italic>Z</jats:italic> = 4 and <jats:italic>R</jats:italic><jats:sub>1</jats:sub> = 0.029. The concept of ‘structural unit’ and ‘interstitial complex’ could be applied to the crystal structure of medvedevite. The structural units in medvedevite are based on the high bond-valence V<jats:sup>5+</jats:sup>O<jats:sub>5</jats:sub> polyhedra which share edges and link into [V<jats:sub>2</jats:sub>O<jats:sub>6</jats:sub>] chains elongated along the <jats:italic>a</jats:italic> axis. The interstitial complexes consist of Mn<jats:sup>2+</jats:sup>, K<jats:sup>+</jats:sup> cations and H<jats:sub>2</jats:sub>O groups and occupy the interstices between structural units. The mineral is optically biaxial (+), with α =1.782(2), β = 1.786(2), γ = 1.792(2), 2V(calc) = 41° (λ = 589 nm). The seven strongest lines of the powder XRD pattern are [<jats:italic>d</jats:italic>, Å (<jats:italic>I</jats:italic>, %) (<jats:italic>hkl</jats:italic>)]: 7.79(100)(011); 5.70(11)(110); 4.75(14)(11<jats:inline-formula><jats:alternatives><jats:tex-math>${2}$</jats:tex-math><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0026461X2200038X_inline1.png" /></jats:alternatives></jats:inline-formula>); 3.89(29)(022); 3.25(53)(031); 2.958(79)(21<jats:inline-formula><jats:alternatives><jats:tex-math>${3}$</jats:tex-math><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0026461X2200038X_inline2.png" /></jats:alternatives></jats:inline-formula>); and 2.850(33)(220). The mineral has been named in honour of the Russian geologist and chemist Robert Alexandrovich Medvedev (1939–2005).</jats:p>

Topics

• impedance spectroscopy
• mineral
• powder X-ray diffraction
• interstitial
• space group