Crednerite from the Gozaisho Mine, Iwaki City, Fukushima Prefecture, Japan

抄録

Crednerite from the Gozaisho mine occurs as black tablets in close association with Sr-bearing barite in a coarse-grained rhodonite ore with minor quartz, braunite, spessartine, aegirine, and ganophyllite, rarely with långbanite as a product of regional metamorphism. The microprobe analysis gives Cu₂O 47.25, Mn₂O₃ 41.78, Fe₂O₃ 10.34, total 99.37%, corresponding to Cu_1.00(Mn_0.80Fe_0.20)_Σ1.00O₂ on the basis of O=2, or ferrian crednerite. The X-ray powder pattern is indexed on a monoclinic cell with a=5.552Å, b=2.894Å, c=5.899Å, β=104.29°, Z=2. The valence loaded ideal formula is Cu¹⁺Mn³⁺O₂. The mineral is not of secondary but primary formation as a metamorphic mineral under the oxidizing condition, which had annihilated Fe²⁺ and influenced the chemical compositions of the associated rhodonite and ganophyllite both devoid of FeO despite their capabilities to involve Fe²⁺. Also, the metamorphic condition enabled the formation of solid solution containing 20 mole% of CuFeO₂, but this was not attained under the superficial oxidizing condition under which all the known crednerites have been formed.