In a project which has been ongoing for several years, a number of rare minerals containing essential Pb or Sb have been studied in terms of their parageneses, chemical composition and crystal structure. Factors critical to their formation in the natural environment have been evaluated and experiments have in certain cases been carried out to prepare synthetic equivalents. Systematic investigations of oxide assemblages, mainly from Lĺngban-type deposits, revealed the existence of several minerals previously unknown to science that we subsequently have formally named and described: Zenzénite, Pb3(Mn3+, Fe)4Mn3O15, forms its own structure type, based on a hexagonal closest-packed array of Pb + O atoms. Lindqvistite, Pb2MnFe16O27 (shown to be an end-member of a new homologous series), and nezilovite, PbZn2(Mn4+, Ti)2Fe8O19, belong to the prolific hexagonal ferrite family. Hiärneite, Ca2Zr4(Zr, Mn3+)(Sb, Ti)2O16, is the sole Zr-Sb-mineral known and isostructural with calzirtite. Tegengrenite, with the structural formula Mn2+12(Si,Ti)2Mg18Sb5+7Mn3+3O56, is closely related to filipstadite, both being ordered variations on the spinel theme. Further descriptions of new minerals are under way.
Crystal structure of zenzénite (polyhedral model) viewed approximately perpendicular
The face-shearing octahedra contain Fe; tri-and tetravalent Mn occupy different octahedra in layers at z=0. The Pb atoms (not shown) reside in the open space at z=0.25.
Photomicrograph of a polished section (transmitted light) with dark red grains of tegengrenite, contiguous to hausmannite (black) and isolated in calcite (colourless).
Field of view is 1.1 x 0.9 mm.
Photo: Dan Holtstam
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