<報文>東北地方産ケイ酸マンガン鉱の鉱物学的研究(第18報) : 岩手県肘葛鉱山産テフロかんらん石について

概要

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Tephroite occurs as aggregates of small prismatic crystals up to 2.5×2.0 mm in the bedded manganese ore deposits of the Hijikuzu mine, in the highly metamorphosed Jurassic quartzite by the intrusion of the Miyako granitic mass. This mineral is associated mainly with rhodonite, manganoan calcite and quartz. The mineral is deep green to dark gray with vitreous luster. In the thin section, mineral is nonpleochroic and very pale greenish color. Optical properties of two varieties of this mineral of "deep green" and "dark gray" are α 1.766,1.762 ; β 1.801,1.800 ; γ 1.814,1.812 ; and 2V_α70°, 68°, respectively. Unit cell constants of these two are a_0 4.889,4.881 ; b_0 10.580,10.567 ; c_0 6.236,6.244 A ; V 322.6,321.3 A^3,respectively. On the basis of 4 oxygen, the chemical analyese of these two varieties yields the formulas as follows ; (Mn_<1.887> Mg_<0.077> Ca<0.023> Fe^<2+>_<0.013> Fe^<3+>_<0.012>Ti_<0.002>) _<2.010> (Si_<0.966>Al_<0.037>) _<1.003>O_<4.000> for the "deep green variety" and (Mn_<1.848>Mg_<0.123>Fe^<2+>_<0.031>Fe^<3+>_<0.021>Ca_<0.018>Ti_<0.004>)_<2.045> (Si_<0.922>Al_<0.065>)_<0.987> O_<4.000> for the "dark gray variety". Both are close to the ideal formula Mn_2SiO_4. The high temperature X-ray examination and differential thermal analysis indicate that the mineral disintegrates to a braunite at about 1,100℃ and changes to a mixture of rhodonite, hausmannite and tridymite at about 1,200℃, in air.
東北大学の論文
1976-03-30