... to the M(1)O 8 cavity. In fact, the calculated BVS at the M(1) site of braunite, neltnerite and abswurmbachite show that only VIII Mn 2+ has the ideal size to fit with the M(1)O 8 cavity. Replacement of Mn 2+ with Zr 4+ , Cu 2+ and Ca 2+ causes the M(1)–O bonds to become strained as indicated...

...Johan P. de Villiers; Peter R. Buseck Abstract Bixbyite, braunite, neltnerite, and braunite-II are members of a mineral group based on the cation arrangement of the fluorite structure type, with general formula M 8 O 12 (M: Mn, Fe, Ca, Si). They consist of layer modules of (Mn,Fe)-O octahedra...

... ) and neltnerite ( Baudracco-Gritti et al. , 1982 ) were described. On a visit to the mine in 1967, French geologist/mineralogist Jacques Emile Dietrich ( Fig. 1 ) collected specimens from the aforementioned area of the mine. Dr. Dietrich brought these specimens back to France in two wooden boxes, which were...

... is generally <0.7 wt% showing the presence of a small amount of neltnerite component (CaMn 3+ 6 SiO 12 : Baudracco-Gritti et al. 1982 ). The Fe 2 O 3 content ranges from 6.1 to 9.1 wt%. Contents of TiO 2 , Al 2 O 3 , BaO, PbO, and SrO are all <0.1, 0.9, 0.3, 0.1, and 0.1 wt%, respectively. T...