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Ca(Fe3+,Mn3+)2Mn4+O6 to marokite super group


Wernerkrauseite is isostructural with Harmunite. Ca-deficient structural analogue of harmunite. Post-spinel structure type.
Crystallisation of wernerkrauseite took place at temperatures below 850–900°C under high oxygen fugacity. (quoted MinDat).

Quote G.Blaß: in a Ca-rich xenolithe from Bellerberg some ingrown small black, longitudinally striped prisms with a strong, metal-like sheen fell on the working name Ca (Mn, Fe) O4-Mineral. First EDX analyzes resulted in the formula Ca1-x (Mn, Fe) 2O4 (with Mn> Fe), which suggested the very rare oxide morocite, CaMn2O4. The solution of the structure on the basis of single crystal X-ray data showed, however, that the mineral from Bellerberg does not crystallize in the structure type and in the space group of Morocite, but in the slightly different structure type of the currently only synthetically known compound CaFe2O4. Furthermore, the structure refinement showed that the Ca position is understaffed and somewhat disordered. The EDX analyzes also showed a lower Ca content compared to the "ideal formula" Ca (Mn, Fe) 2O4. The assumption that it is a new mineral has now been confirmed by the IMA as Wernerkrauseit (IMA No. 2014-008). As mentioned above, the Wernerkrauseit was found as inclusions in a weathered, Ca-rich, blue and yellow speckled xenolite from the Bellerberg volcano (Stbr. Caspar). The new mineral forms black, shiny metallic, long prismatic to needle-like elongated crystals. They are usually stored in the Ca-rich matrix and free-broken, idiomorphic crystals only rarely appear. They are up to about 1 millimeter long and have characteristic striations parallel to the longitudinal axis and are typically also grown together in parallel (picture). Internal adhesions with magnesia ferrite and perovskite could also be detected in the section. The primary mineral components gehlenite, fluorellestadite, wadalite, lakargiite and others as well as their weathering products ettringite-thaumasite, hydrocalumite, jennite and katoite could be detected as additional accompanying minerals. Furthermore, the two minerals Pavlovskyite and Rusinovite were determined in the matrix for the first time for the Bellerberg.


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