島根県銅ヶ丸鉱山および滋賀県御池鉱山産ハイドロウッドワード石の化学組成

抄録

  Four hydrowoodwardite samples, simplified formula [Cu_1−xAl_x(OH)₂](SO₄)_x/2•mH₂O (0.03≦x≦0.38)], collected from the Dogamaru mine, Shimane Prefecture and the Oike mine, Shiga Prefecture were characterized by powder X-ray diffraction, Fourier transform infrared (FT-IR) and electron microprobe analyses. The samples obtained from the Dogamaru and Oike mines occur as green to blue colloidal crusts (0.5 mm to 20 mm in thickness). The samples indicate fine bedded texture (1 μm to 10 μm in thickness) corresponding to the different compositions. Powder X-ray diffraction patterns are close to those of hydrowoodwardite. FT-IR spectra showed absorption bands at around 3450 cm⁻¹ due to O-H stretching vibration, at around 1640 cm⁻¹ due to H-O-H bending vibration, at around 1100 cm⁻¹ due to v₃ and v₁ SO₄²⁻ stretching vibrations, and at around 620 cm⁻¹ and 470 cm⁻¹ due to v₄ and v₂ SO₄²⁻ bending vibrations, respectively. Weak absorption bands at around 1395 cm⁻¹ due to carbonate group are observed in the Dogamaru samples. Electron microprobe analyses revealed that the main components are Cu, Al, S, and Si; Si is derived from amorphous silica. Small amount of Zn is contained in the Dogamaru samples. The predominant mechanism for changes in chemical composition of the each sample is substitution of Al for Cu with constant Zn ratios. The ranges of Cu, Zn, Al, and S (apfu) in the Dogamaru and Oike samples are as follows: Cu 0.53–0.89 and 0.62–0.96; Zn 0.03–0.17 and 0.00–0.01; Al 0.04–0.38 and 0.03–0.38; and S 0.02–0.16 and 0.02–0.17, respectively. The minimum values of Al are smaller than any of previously reported hydrowoodwardite.