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.