Manjiroite, a new manganese dioxide mineral, from Kohare Mine, Iwate Prefecture, Japan

要旨

Manjiroite, a new manganese dioxide mineral, occurs in the oxidation zone of rhodonite-tephroite-rhodochrosite bedded ore deposits of Kohare Mine, Iwate Prefecture, Japan, running along the boundaries between chert and schalstein of Permian age. It is associated with pyrolusite, nsutite, birnessite, cryptomelane and goethite. Manjiroite is dense compact masses up to 10×8×5cm., with marked conchoidal fracture. Colour dark brownish-gray, luster dull, streak brownish-black. No cleavage, sp. gr. 4.29, Vickers hardness 181 av. Under the microscope opaque, distinctly anisotropic with weak pleochroism. Analysis gives MnO2 85.79, MnO 3.17, CuO 0.03, CoO none, ZnO 0.03, MgO 0.18, CaO 0.22, Na2O 2.99, K2O 1.39, BaO 0.16, Al2O3 0.62, Fe2O3 0.40, TiO2 none, SiO2 0.12, H2O- 0.68, H2O+3.92, sum 99.71%. This corresponds to (Na0.73 K0.22 Ca0.03 Ba0.01) 0.99 (Mn4+7.46 Mn2+0.34 A10.09 Fe0.04 Mg 0.03) 7.96 O16⋅1.64H2O or (Na, K) Mn4+8 O16⋅nH2O (probably n<2). The DTA curve shows endothermal effects at 530°, 905°, and 980°C. X-ray study shows it to be tetragonal, aO 9.916, cO 2.864A, isostructural with cryptomelane. There is probably an isomorphous series between cryptomelane and majiroite. The strongest lines of the X-ray pattern are 2.406 (100) (121), 7.02 (98) (110), 3.14 (92) (130), 4.94 (77) (200), 2.160 (69) (301), 1.839 (46) (141), 1.548 (46) (251), 2.332 (38) (330), 1.431 (38) (002). The name is given in honour of Dr. Manjiro Watanabe, mineralogist, economic geologist and Emeritus Professor of Tohoku University, Japan. The mineral, Manjiroite, has been approved by the Commission on New Mineral and Mineral-Name, I. M. A.

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