岩手県赤金鉱山産新鉱物赤金鉱(β-FeOOH)について

抄録

The new mineral akaganeite is beta-ferric oxyhydroxide from the weathered outcrop of the Akagane pyrometasomatic copper-iron deposit in Carboniferous green rock, Iwate Prefecture, Japan. The mineral is the supergene oxidation product of massive pyrrhotite and intimately associated with goethite, melantilite and two kinds of ferric sulfates. The mineral occurs in powdery aggregates of very fine orange to brownish-yellow crystals, elongated [001] and flattened (100) up to 0.3×0.03μ in size under the electron microscope.
Two chemical analyses carried out in 1956 and 1959, respectively: Fe₂O₃ 78.23, 80.98; FeO 0.82, 0.23; SiO₂ 3.10, 3, 57; A1₂O₃ 1.21, 1.40; Na₂O 0.62, 0.82; K₂O 0.19, 0.29; H₂O+ 10.20, 9.71; H₂O- 4.96, 2.55, sum 99.33, 99.55%. These data correspond closely to FeOOH. Chlorine was detected qualitatively, but material was in sufficient for a quantitative analysis.
X-ray powder data are indexed on a tetragonal cell with a=10.50, c=3.03A. The strongest lines are 7.45 (98) (110), 5.31 (48) (200), 3.71 (21) (220), 3.34 (100) (310), 2.361 (33) (400), 2.553 (95) (211), 2.340 (8) (420), 2.300 (43) (301), 2.103 (31) (321), 1.954 ((39) (411), 1.750 (42) (600), 1.720 (12) (501, 431), 1.646 (52) (521), 1.520 (21) (002), 1.456 (28) (640), 1.441 (30d) (1.438), 1.381 (40d) (730, 312). These data agree very closely with the data obtained by Macky (1960), who showed the synthetic β-FeOOH is tetragonal, 14/m, a=10.48, c=3.023A. A DTA curve showed a slight endothermal reaction at about 300°C and a marked exothermal peak at 375°C. The mineral loss 11% in weight to 350°C, nearly all between 250 and 350°C.
The name is for the mine. The mineral and name were aproved before publication by the Commission on New Minerals and Mineral Names, IMA.
Two short communications on akaganeite have been described in Japanese by the present author (1957, 1960).