Plumboferrite from the type locality at Jakobsberg, Filipstad, Sweden, has been reexamined. It occurs in assemblages confined to bands in metamorphic carbonate rock and is associated with hematite, magnesioferrite-jacobsite-magnetite solid solutions, lindqvistite, calcite, andradite, phlogopite, hedyphane, svabite, hematophanite, native copper, and cuprite. Six samples investigated fall in a narrow composition range: PbO 33.9–34.6, Sb2O5 0.0–0.3, Fe2O3 62.4–63.9, MnO 0.6–1.8, TiO2 0.1–0.5, SiO2 0.0–0.2, Al2O3 0.0–0.1, MgO 0.1–0.4 (weight percent). The mineral is moderately anisotropic and optically uniaxial (−). Reflectance values obtained in air are 25.6–24.2% (470 nm), 24.5–23.5% (546 nm), 23.7–22.8 (589 nm), and 22.6–22.1% (650 nm). VHN100 = 882 and Dcalc = 6.12(1) g/cm3.
Single-crystal X-ray studies show that plumboferrite is hexagonal, essentially P63/mmc, with the cell dimensions a = 5.931(1), c = 23.551(2) Å, and V = 717.4(2) Å3 (refined from powder data). Overexposed precession X-ray photographs indicate the presence of a supercell with Å and c′ = 3c = 70.7 Å (hexagonal setting). The structure of plumboferrite has been refined from the 394 most significant (I > 5σI) X-ray reflections with (sin θ)/λ ≤ 0.81 Å−1 to R = 3.9%. It has a defect magnetoplumbite-type structure that can be described in terms of two basic structural units, the R and the S (spinel) blocks. The stacking sequence of such blocks along c is RSR′S′, where ideally R = (Pb2Fe5O11−δ) and S = (Fe6O8) for plumboferrite. The formula (with Z = 2 for the subcell) for the investigated material approaches Pb2Me0.33Fe10.67O18.33, with Me = Mn2+, Mg, rather than PbFe4O7, which is still prevalent in the literature. The departure from stoichiometry (19 O atoms per formula unit) reflects partially occupied 03 positions in the R blocks. The weak superlattice reflections observed (not included in the present refinements) probably result from the ordering of split Pb positions, O vacancies, or both.