New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. XIV. Badalovite, NaNaMg(MgFe3+)(AsO4) a member of the alluaudite group

The new alluaudite-group mineral badalovite was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with hematite, tenorite, cassiterite, johillerite, nickenichite, calciojohillerite, bradaczekite, metathenardite, aphthitalite, langbeinite, calciolangbeinite, sanidine, fluorophlogopite, fluoborite, tilasite, anhydrite, pseudobrookite, sylvite, halite, lammerite, urusovite, ericlaxmanite, arsmirandite, svabite, krasheninnikovite, euchlorine, wulffite and alumoklyuchevskite. Badalovite forms oblique-angled prismatic crystals up to 1 mm x 1 mm x 5 mm, typically combined in groups or crusts up to several hundred cm(2 )in area. The mineral is transparent, green, grey, yellow or colourless, with vitreous lustre. It is brittle, the Mohs hardness is 31/2. Cleavage was not observed, the fracture is uneven. D-calc is 4.02 g cm(-3). Badalovite is optically biaxial (-), alpha = 1.753(3), beta = 1.757(3), gamma = 1.758(3) and 2V(max) = 50(10)degrees. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 9.23, K2O 0.19, CaO 2.04, MgO 13.78, MnO 0.31, CuO 0.12, ZnO 0.24, Al2O3 0.06, Fe2O3 12.77, TiO2 0.01, SiO2 0.06, P2O5 0.33, V2O5 0.05, As2O5 61.51, SO3 0.02, total 100.72. The empirical formula based on 12 O apfu is Na1.67Ca0.20K0.02Mg1.92Zn0.02 Mn0.02Cu0.01Fe0.903+Al0.01(As3.01P0.03Si0.01)Sigma O-3.03(12). The simplified formula is Na2Mg2Fe3+ (AsO4)(3). Badalovite is monoclinic, C2/c, a =11.9034(3), b= 12.7832(2), c= 6.66340(16) angstrom, beta = 112.523(3)degrees, V= 936.59(4) angstrom(3) and Z = 4. The strongest reflections of the powder XRD pattern [d,angstrom(I)(hkl)] are: 6.41(38)(020), 5.505(20)(200), 3.577(23)((1) over bar 31), 3.523(25)(310), 3.211(46)((1) over bar 12), 2.911(28)((2) over bar 22, (3) over bar 12), 2.765(100)(240, 400) and 2.618(26)((1) over bar 32). The crystal structure was solved from single-crystal XRD data with an R-1 of = 2.49%. Badalovite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is Na-A(1)(A(1)), square(A(2)), square(A(2)),(NaMgM(2))-Na- -Mg-M(1)(Mg0.5Fe0.53+)(2)(AsO4)(3)(square - vacancy) and the end-member formula is NaNaMg(MgFe3+)(AsO4)(3). The mineral is named in honour of the outstanding mineralogist and geochemist Stepan Tigranovich Badalov (1919-2014).