Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Jakub Plášil, Pavel Škácha, Jiří Sejkora, Radek Škoda, Milan Novák, František Veselovský, Jan Hloušek

Babánekite, Cu₃(AsO₄)₂ ∙ 8H₂O, from Jáchymov, Czech Republic - a new member of the vivianite group

Journal of Geosciences, volume 62 (2017), issue 4, 261 - 270

DOI: http://doi.org/10.3190/jgeosci.248

Babánekite, Cu₃(AsO₄)₂∙8H₂O, a new member of the vivianite group was found in material originating from the Geister vein, Rovnost mine, Jáchymov, Western Bohemia, Czech Republic. It occurs as a supergene alteration mineral in association with members of the lindackerite supergroup (veselovskýite, hloušekite, pradetite and lindackerite), lavendulan, gypsum and an X-ray amorphous Cu-Al-Si-O-H phase. Crystals of babánekite are pinkish to peach-colored, elongated, prismatic and up to 2 mm in length. They exhibit the forms {010}, {100}, {110}, {101} and less frequently also {001}. Crystals are transparent to translucent with a vitreous luster. The mineral has a light pinkish streak. Estimated Mohs hardness is between 1.5 and 2. The cleavage is perfect on {010}. The calculated density is 3.192 g/cm³. Electron-microprobe analysis yielded CoO 8.89, NiO 4.06, CuO 15.31, ZnO 10.87, P₂O₅ 0.16, As₂O₅ 39.79, SO₃ 0.13, H₂O 24.78 (calc.), total 103.99 wt.% yielding the empirical formula (Cu_1.12Zn_0.78Co_0.69Ni_0.32)_Σ2.91[(AsO₄)_2.01(PO₄)_0.01(SO₄)_0.01]_Σ2.03∙8H₂O based on 16 O apfu. The ideal end-member formula of babánekite is Cu₃(AsO₄)₂ ∙8H₂O, which requires CuO 38.95, As₂O₅ 37.52, H₂O 23.53, total 100.00 wt.%. Babánekite is monoclinic, C2/m, with a = 10.1729(3), b = 13.5088(4), c = 4.7496(1) Å, β = 105.399(2)°, V = 629.28(3) ų and Z = 2. The eight strongest X-ray powder diffraction lines are [d_obs Å(I)(hkl)]: 7.936(11)(110), 6.743(100)(020), 3.231(14)(13-1), 2.715(11)(041), 2.3331(10)(15-1), 2.0819(5)(350), 1.6862(16)(080) and 1.6107(4)(55-1). The crystal structure of babánekite, refined to R₁ = 2.18 % for 864 unique observed reflections, confirmed that the atomic arrangement is similar to other members of the vivianite group of minerals. The mineral is named for Ing. František Babánek (1836-1910), Czech mining and geological expert, who worked in the Jáchymov and Příbram mines.