Igelströmite, Fe³⁺(Sb³⁺Pb²⁺)O₄, and manganoschafarzikite, Mn²⁺Sb³⁺₂O₄, two new members of the newly established minium group, from the Långban Mn–Fe deposit, Värmland, Sweden

Abstract

The two new minerals igelströmite, Fe3+(Sb3+Pb2+)O4, and manganoschafarzikite, Mn2+Sb23+O4, are found in the Långban Fe–Mn deposit, in open fractures in a fine-grained hematite ore, with minor amounts of aegirine, a serpentine-group mineral, fluorcalcioroméite, baryte, nadorite, mimetite and other late-stage minerals. Igelströmite is named after the Swedish geologist–mineralogist Lars Johan Igelström (1822–1897). Mohs hardness = 3–4 and Dcalc= 6.33(1) and 5.37(2) g cm−3 for igelströmite and manganoschafarzikite, respectively. Cleavage is distinct on {110}. Both minerals are brittle, with an uneven to conchoidal fracture. The chemical formulae obtained from microprobe data are (Fe0.593+Mn0.292+As0.063+Fe0.062+)Σ=1.00(Sb1.243+Pb0.652+As0.113+)Σ=2.00O4 and (Mn0.642+Fe0.252+Mg0.08)Σ=0.97(Sb1.973+As0.033+Pb0.012+)Σ=2.01O4. The crystal structures for igelströmite and manganoschafarzikite have been refined in space group P42/mbc from single-crystal X-ray diffraction data to R1 = 3.73 % and 1.51 %, respectively, giving the following sets of unit-cell parameters: a= 8.4856(2), 8.65159(8) Å; c= 6.0450(3), 5.97175(9); and V= 435.27(3), 446.986(11) Å3 for Z = 4. Both minerals are isostructural with minium, Pb4+Pb22+O4, where Pb4+O6 forms distorted octahedra, which connect via trans-edges to form rutile-like ribbons along c. The Pb2+ atoms appear in trigonal, flattened PbO3 pyramids, which are linked via corners to form zigzag (PbO2)n chains. The minium group, of general formula MX2O4(X= As3+, Sb3+, Pb2+), presently consists of the minerals minium, trippkeite, schafarzikite, igelströmite and manganoschafarzikite. For future new members, it is recommended to consider the X cation content for the root name and add prefixes to indicate the dominant metal at the M position.