Acta Musei Moraviae

Neustädtelite from Moldava, Krušné hory Mountains (Czech Republic)

A rare mineral neustädtelite, Bi₂Fe³⁺Fe³⁺O₂(OH)₂(AsO₄)₂, was found in material from the mine dump of now abandoned Moldava fluorite deposit, Krušné hory Mountains, northern Bohemia. This is the second occurrence of this mineral in the Czech Republic. Neustädtelite occurs there as light brown crystalline coatings covering on the area of some mm², formed by elongated tabular crystals 5–30 μm in size in association with acanthite, fluorite, quartz, preisingerite and mixite. Neustädtelite is triclinic, space group P-1, with the unit-cell parameters refined from X-ray powder diffraction data: a 4.5620(19), b 6.1564(19), c 9.011(3) Å, α 95.39(3), β 99.31(3), γ 92.86(3)° and V 248.09(16) ų. Chemical analyses of neustädtelite correspond to the empirical formula (Bi_1.87Pb_0.08Ca_0.08)Σ_1.97Fe³⁺ _1.00(Fe_0.58Ni_0.19Co_0.13Cu_0.10Zn_0.10)Σ_1.10(AsO₄)_1.83(PO₄)_0.07(SO₄)_0.10]Σ_2.00[O_1.58(OH)_2.74]Σ_4.32, calculated based on the sum of As+P+S = 2 apfu. Its origin is connected with simultaneous weathering of primary tennantite, bismuth, galena and Ni-Co arsenides in the conditions of supergene zone in-situ.