Jôkokuite, MnSO₄·5H₂O, a new mineral from the Jôkoku Mine, Hokkaido, Japan

Abstract

Jôkokuite, MnSO₄·5H₂O, is a new hydrous manganese sulfate discovered at the drift wall of the 50 m level of the Jôkoku manganese-lead-zinc mine, southwestern Hokkaido. It occurs as post-mine stalactites up to about 5 cm long and 1 cm across, apparently precipitated secondarily from mine waters carrying components from manganese carbonates consisting mainly of rhodochrosite and manganoan calcite.
X-ray powder diffraction pattern shows that it is triclinic with a=6.37Å, b=10.77Å, c=6.13Å, α=98^°46′, β=109^°58′, γ=77^°50′, Z=2, and space group P-1 seems probable from the analogy with chalcanthite (CuSO₄·5H₂O). Wet chemical analysis gives the formula of (Mn_0.93Fe_0.04Zn_0.03)_1.00S_1.00O_4.00·5.07H₂0, or ideally MnSO₄·5H₂O. Therefore, this is the manganese analogue of chalcanthite, pentahydrite and siderotil.
The mineral is pale pink with vitreous luster, and transparent to translucent. Streak is white. No discernible cleavage. Mohs hardness of aggregates is about 2.5. Specific gravity is 2.03 (meas.) and 2.094 (calc). It is biaxial and optically negative, 2V about 70–80°, dispersion very weak. The indices of refraction are α=1.498, β=1.510, γ=1.517, all±0.003.