Iwakiite, Mn²⁺(Fe³⁺, Mn³⁺)₂O₄, a new tetragonal spinelloid mineral from the Gozaisho mine, Fukushima Prefecture, Japan

Abstract

Iwakiite, Mn²⁺(Fe³⁺, Mn³⁺)₂O₄, is tetragonal, space group P4₂⁄nnm, a 8.509, c 8.534Å, Z=8, and is found in rhodonite-quartz ore from the regionally metamorphosed manganese ore deposit of the Gozaisho mine, Fukushima Prefecture, Japan.
Wet chemical analysis by K. N. gave MnO 30.34, MgO 0.61, Mn₂O₃ 22.70, Fe₂O₃ 44.42, Al₂O₃ 0.32, SiO₂ 0.47, TiO₂ 0.30, SrO 0.04, Na₂O 0.02, K₂O 0.02, total 99.24%, corresponding to (Mn²⁺_0.982Mg_0.035)_Σ=1.017(Fe³⁺_1.277Mn³⁺_0.660Si_0.018 Al_0.014Ti_0.009)_Σ=1.978O₄ on the basis of O=4, or ideally Mn²⁺(Fe³⁺, Mn³⁺)₂O₄, where Fe³⁺:Mn³⁺=2:1. The strongest X-ray powder diffractions are 4.929(30) (111), 3.016(40) (202, 220), 2.570(100) (113, 311), 1.640(30) (333), 1.509(35) (404), 1.506(40) (440). They are similar to but distinct from those of jacobsite due to splitting of (404)–(440).
It is opaque. Colour is greenish black, lustre metallic. Streak is black. No cleavage. Density (g/cm³) 4.85 (meas.), 4.89 (calc.). Strongly magnetic. It is optically anisotropic. The reflection colour in air is olive grey like jacobsite without discernible reflection pleochroism. Between crossed polars the colour changes from yellowish to brownish grey.
The name is for the city name Iwaki, in which the locality is situated. Type material is deposited in National Science Museum, Shinjuku, Tokyo, Japan.