Lindqvistite, Pb (sub 2) MeFe (sub 16) O (sub 27) , a novel hexagonal ferrite mineral from Jakobsberg, Filipstad, Sweden

Lindqvistite is a new mineral from Jakobsberg, Filipstad, Sweden. It occurs as black crystals <= 5 mm in size with perfect basal cleavage, associated with hematite, jacobsite, plumboferrite, calcite, phlogopite, andradite, hedyphane, baryte and copper minerals. The mineral is opaque, grey in reflected light, with weak bireflectance and is moderately anisotropic. Reflectance values obtained in air and oil (at 589 nm) are R (sub o) = 22.2, R (sub e') = 21.5, (super im) R (sub o) = 8.76, and (super im) R (sub e') = 8.34%. VHN (sub 100) = 857 and D (sub calc) 5.76(1) g/cm (super 3) . The idealized formula for lindqvistite is Pb (sub 2Me) Fe (sub 16) O (sub 27) , with Me = Mn (super 2+) , Mg. X-ray studies show that lindqvistite is hexagonal, essentially P6 (sub 3) /mmc, with a 5.951(1), c 33.358(4) Angstrom, and V 1023.1(5) Angstrom (super 3) for Z = 2. The most intense reflections in the X-ray powder pattern are 2.624(100), 2.802(95), 2.612(90), 2.975(70), 3.011(60) Angstrom . Very weak diffuse extra reflections, about two orders of magnitude weaker than the substructure reflections, observed on X-ray photographs could be indexed with a tripled hexagonal unit cell (a' = a square root 3 = 10.31 Angstrom and c' = c). The present investigation is confined to elucidating the substructure having a 5.951 Angstrom . The derived structural model of lindqvistite has been refined, with the 505 most significant X-ray reflections to R = 0.041. It is closely related to the W-type synthetic ferrites and can be described in terms of two basic structural units, commonly denoted as the R and the S (spinel) blocks. The stacking sequence of such blocks is RSSR'S'S', where R = (Pb (sub 2) Fe (sub 5) O (sub 11) ) (super 3-) and S = (Me (sub 0.5) Fe (sub 5.5) O (sub 8) ) (super 1.5+) for lindqvistite. The two crystallographically different Pb atoms and a single O atom, all located at the central section of the R block, are positionally disordered. The mineral name honours Bengt Lindqvist of the Swedish Museum of Natural History, where the type material is deposited.