• Spratt, John

Abstract

<jats:title>Abstract</jats:title><jats:p>Dokuchaevite, ideally Cu<jats:sub>8</jats:sub>O<jats:sub>2</jats:sub>(VO<jats:sub>4</jats:sub>)<jats:sub>3</jats:sub>Cl<jats:sub>3</jats:sub>, was found in the Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Dokuchaevite occurs on the crusts of various copper sulfate exhalative minerals (such as kamchatkite and euchlorine) as individual prismatic crystals. Dokuchaevite is triclinic, <jats:italic>P</jats:italic><jats:inline-formula><jats:alternatives><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S0026461X19000410_inline1" /><jats:tex-math>${1}$</jats:tex-math></jats:alternatives></jats:inline-formula>, <jats:italic>a</jats:italic> = 6.332(3), <jats:italic>b</jats:italic> = 8.204(4), <jats:italic>c</jats:italic> = 15.562(8) Å, α = 90.498(8), β = 97.173(7), γ = 90.896(13)°, <jats:italic>V</jats:italic> = 801.9(7) Å<jats:sup>3</jats:sup> and <jats:italic>R</jats:italic><jats:sub>1</jats:sub> = 0.057. The eight strongest lines of the X-ray powder diffraction pattern are (<jats:italic>d</jats:italic>, Å (<jats:italic>I</jats:italic>)(<jats:italic>hkl</jats:italic>): (15.4396)(18)(00<jats:inline-formula><jats:alternatives><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S0026461X19000410_inline2" /><jats:tex-math>${1}$</jats:tex-math></jats:alternatives></jats:inline-formula>), (7.2762)(27)(0<jats:inline-formula><jats:alternatives><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S0026461X19000410_inline3" /><jats:tex-math>${1}$</jats:tex-math></jats:alternatives></jats:inline-formula>1), (5.5957)(43)(012), (4.8571)(33)(<jats:inline-formula><jats:alternatives><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S0026461X19000410_inline4" /><jats:tex-math>${1}{1}$</jats:tex-math></jats:alternatives></jats:inline-formula>1), (3.1929) (29)(023), (2.7915)(30)(202), (2.5645)(21)(032), (2.5220)(100)(1<jats:inline-formula><jats:alternatives><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S0026461X19000410_inline5" /><jats:tex-math>${3}$</jats:tex-math></jats:alternatives></jats:inline-formula>0), (2.4906)(18)(130) and (2.3267)(71)(2<jats:inline-formula><jats:alternatives><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="gif" xlink:type="simple" xlink:href="S0026461X19000410_inline6" /><jats:tex-math>${2}$</jats:tex-math></jats:alternatives></jats:inline-formula>2). The chemical composition determined by electron-microprobe analysis is (wt.%): CuO 60.87, ZnO 0.50, FeO 0.36, V<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> 19.85, As<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> 6.96, SO<jats:sub>3</jats:sub> 0.44, MoO<jats:sub>3</jats:sub> 1.41, SiO<jats:sub>2</jats:sub> 0.20, P<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> 0.22, Cl 10.66, –O = Cl<jats:sub>2</jats:sub> 2.41, total 99.06. The empirical formula calculated on the basis of 17 anions per formula unit is (Cu<jats:sub>7.72</jats:sub>Zn<jats:sub>0.06</jats:sub>Fe<jats:sub>0.05</jats:sub>)<jats:sub>Σ7.83</jats:sub>(V<jats:sub>2.20</jats:sub>As<jats:sub>0.61</jats:sub>Mo<jats:sub>0.10</jats:sub>S<jats:sub>0.06</jats:sub>P<jats:sub>0.03</jats:sub>Si<jats:sub>0.03</jats:sub>)<jats:sub>Σ3.03</jats:sub>O<jats:sub>13.96</jats:sub>Cl<jats:sub>3.04</jats:sub>.</jats:p><jats:p>The crystal structure of dokuchaevite represents a new structure type with eight Cu sites, which demonstrate the remarkable diversity of Cu<jats:sup>2+</jats:sup> mixed-ligand coordination environments. The crystal structure of dokuchaevite is based on OCu<jats:sub>4</jats:sub> tetrahedra that share common corners thus forming [O<jats:sub>2</jats:sub>Cu<jats:sub>6</jats:sub>]<jats:sup>8+</jats:sup> single chains. Two of the eight symmetrically independent copper atoms do not form Cu–O bonds with additional oxygen atoms, and thus are not part of the OCu<jats:sub>4</jats:sub> tetrahedra, but provide the three-dimensional integrity of the [O<jats:sub>2</jats:sub>Cu<jats:sub>6</jats:sub>]<jats:sup>8+</jats:sup> chains into a framework. <jats:italic>T</jats:italic>O<jats:sub>4</jats:sub> mixed tetrahedral groups are located within the cavities of the framework. The structural formula of dokuchaevite can be represented as Cu<jats:sub>2</jats:sub>[Cu<jats:sub>6</jats:sub>O<jats:sub>2</jats:sub>](VO<jats:sub>4</jats:sub>)<jats:sub>3</jats:sub>Cl<jats:sub>3</jats:sub>.</jats:p>

Topics

• impedance spectroscopy
• mineral
• Oxygen
• chemical composition
• copper
• forming