<Original Papers>Mineralogical Study of Manganese Silicate Ores in Northeastern Japan. (XXVI) : Manganese and Iron Rich Saponite from Noda-Tamagawa Mine, Iwate Prefecture

Manganese and iron rich saponite occur as aggregates of fine particles filling the fracture zone of the fault which cuts the rhodonite-tephroite-pyrochroite ore body at L1N95 of Misago bedded manganese ore deposits of the Noda-Tamagawa mine, in the highly metamorphosed Jurassic quartzite by the intrusion of the granitic mass. They are black in color and very pale brownish in thin section. The basal reflection shfits form 15.3A to 17.0A from treatment with ethylen glycol, and the spacing of (06,33) is 1.535A. Thus the X-ray powder pattern of this type is very close to those of trioctahedral smectite. Chemical analysis gives : SiO_2 37.19,TiO_2 0.00,Al_2O_3 3.61,Fe_2O_3 8.14,FeO 0.00,MnO 11.62,MnO_2 2.58,MgO 8.51,CaO 2.00,Na_2O 0.53,K_2O 0.10. H_2O^+ 6.86,H_2O^- 18.53,total 99.67 wt.%. If the empirical formula is made through chemical analysis, the octahedral coordination is 5.41,which is between di- and trioctahecral smectite, and some amounts of Fe^ must have the tetrahedral coordination. Then, it is postulated that all Fe^ and Mn^ were derived from Fe^ and Mn^ by natural oxidation, the following empirical formula was made by converting all Fe^ into Fe^ and Mn^ into Mn^ : {Na_ K_ (Ca/2)_}_ (Mg_Mn^_Fe^_Al_)_ [Si_Al_]_O_(OH)_2・2.5H_2O. In this case, the number of ions having an octahedral coordination is 6.01,and this formula corresponds to that of manganese and iron rich saponite, in which 58% of Mg ion of usual saponite replaced by 38% of Mn^ and 20% of Fe^. The mineral is a variety having more Mn^ content than any examples ever known