<Original Papers>Mineralogical Study of Manganese Silicate Ores in Northeastern Japan. (XXIX) : Caryopilite-like Mineral from Noda-Tamagawa Mine, Iwate Prefecture

Caryopilite-like mineral occurs as lenticular aggregate of very fine crystals in rhodonite-tephroite ore-body at L13 of Misago bedded manganese ore deposits of the Noda-Tamagawa mine, in highly metamorphosed Jurassic quartzite by the intrusion of the granitic mass. It is black in color and colorless to very pale yellow-brown in thin section. Chemical analysis gives : SiO_2 34.65,TiO_2 0.00,Al_2O_3 0.00,Fe_2O_3 0.57,FeO 0.00,MnO 24.77,Mn_2O_3 0.99,MnO_2 10.79,MgO 11.77,CaO 0.57,Na_2O 0.12,K_2O 0.36,H_2O+ 9.68,H_2O- 5.49,total 99.76%. If it is postulated that all Mn^ and Mn^ were derived from Mn^ by natural oxidation, the following empirical formula can be made by converting all Mn^ and Mn^ into Mn^ : (Mn^_ Mg_ Ca_ K_ Na_ Fe^_)_ Si_ O_ (OH)_, which coresponds closely to the general formula for caryopilite : Mn_ Si_4 O_ (OH)_. The (0k0) and (00l) reflections of the mineral are 7.40 (001), 4.58 (020), 3.66 (002) and 1.531 (060) A. Thus the X-ray powder pattern of this type is closer to that of lizardite than to that of caryopilite. High temperature X-ray studies indicate that the mineral breaks down to a mixture of braunite + clinopyroxene (Mn, Mg)_2 Si_2 O_6 + Mg-pyroxmangite at about 950℃ and it changes to Mg-tephroite + Mg-rhodonite + Mg-pyroxmangite + braunite at about 1,150℃, in air