Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XXI, No.4


Inesite from the Kokuriki Mine, Hokkaido, Japan

Togari, Kenji;Akasaka, Masahide;Kawaguchi, Yoshiyuki

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Inesite occurs in veinlet cutting hematite ore from the Kokuriki mine, eastern Hokkaido. Its associated minerals are rhodochrosite, barite and quartz. The inesite forms fine prisms up to 1 mm long and is pale orange in color. Refractive indices are: α=1.618(3), β=1.639(3) and γ=1.656(3). Biaxial, negative. 2V(meas.)=67-70°. The composition is as follows: SiO2 45.94, Al2O3 0.02, Fe2O3 0.57, MnO 37.50, MgO 0.10, CaO 8.60, Na2O 0.04, K2O 0.04, H2O 8.90, Total 101.71 wt.%. The H2O content was determined by a thermogravimetric analysis. The empirical formula is calculated as: (Ca1.97Na0.02K0.01)Σ2.00(Mn6.80Mg0.03) Σ6.83-(Si9.84Fe3+0.09Al0.01)Σ9.94O35.00H12.72. Unit-cell parameters based on morphological cell were determined by X-ray powder diffraction as follows: a=8.938(4), b=9.259(5), c=11.959(5)Å, a=91.96(7)°, β=132.72(3)°, γ=94.36(6)°. Crystal field spectra indicate that the orange color of the inesite may be caused by Mn3+ converted from a part of Mn2+ .