<Original Papers>Mineralogical Study of the Manganese Silicate Ores in Northeastern Japan. (XVII) : Nambulite from Ohtaniyama Mine, Iwate Prefecture

Nambulite occurs as banded aggregates of small prismatic crystals up to 0.50×0.25 mm in size, in braunite ore body at No.3 Koryu drift of Osono bedded manganese ore deposit of Ohtaniyama mine, in the low grade metamorphosed chert of Permian age. The color is brownish red, specific gravity 3.47 (meas.) and Mohs hardness 6.5. In the thin section, minerals is non-pleochroic, indices of refraction are α 1.705,β 1.709 γ 1.731,γ-α 0.026,and optic axial angle is 2V_γ=30°. On the basis of 15 (O, OH), the chemical analysis yields the formula (Li_ Na_ K_)_ (Mn_ Ca_ Mg_ Li_ Fe_^ Al_)_ Si_ O_ (OH)_, which corresponds closely to theoretical formula (Li, Na) Mn_4 Si_5 O_14 (OH). The high temperature X-ray study and differential thermal analysis indicate that the mineral breaks down to a mixture of braunite+silica O+tridymite at about 800℃ and they change to rhodonite at about 1,080℃, in air