Taneyamalite, a new manganese silicate mineral from the Taneyama mine, Kumamoto Prefecture, Japan

抄録

Taneyamalite is triclinic, space group P1 or P-1, unit cell parameters: a=10.1882±0.0012, b=9.7544±0.0006, c=9.5674±0.0011 Å, α=90.429°±0.019°, β=71.025°±0.014°, γ=109.168°±0.007°, V=844.03±0.13 ų, Z=1. Principal powder lines (d in Å) with relative intensities and indices are: 9.155(100) (010), 7.948(22) (-110), 4.578(15) (020), 3.614(13) (120), 3.252(37) (-130), 3.067(17) (-230), 2.774(24) (220), 2.665(18) (3-13), 2.202(21) (230), 1.696(17) (5-43), 1.686(12) (150). Wet chemical analysis gives: SiO₂ 40.32, TiO₂ 0.05, Al₂O₃, 2.08, Fe₂O₃ 8.68, FeO 11.88, MnO 23.83, MgO 2.50, CaO 0.53, Na₂O 1.63, K₂O 0.10, H₂O⁺ 6.99, H₂O⁻ 0.73, total 99.32%, corresponding to (Na_0.91Ca_0.16K_0.04)_Σ1.11 (Mn²⁺₅₀₇₈Mg_1.07Fe²⁺_2.85Fe³⁺_1.87Al_0.26)_Σ11.83 (Si_11.55 Al_0.44 Ti_0.01)_Σ12.00(O_30.63 (OH)_13.37)_Σ44.00 on the basis of O+OH=44. The ideal formula is (Na, Ca) (Mn²⁺, Mg, Fe²⁺, Fe³⁺, Al)₁₂ (Si, Al)₁₂ (O, OH)₄₄, where Na and Mn²⁺ are the most dominant species in the respective sites. Therefore, taneyamalite is a Mn²⁺-dominant analogue of howieite. It is dark brown to black ni color, luster vitreous. Streak brown. Good (010) and fair (100) cleavages. Mohs’ hardness of the aggregate is 5–6. Specific gravity 3.30 (meas.), density 3.34 (calc. on unit cell data) and 3.31 (calc. on Gladstone-Dale’s law). It is optically biaxial, negative, 2V about 70°, refractive indices α=1.697, β=1.720, γ=1.732. Pleochroism and absorption are X=pale golden yellow, Y=yellowish brown, Z=dark brown; X<Y<Z. Infrared spectrum shows strong absorptions at 3525, 3420, 1029, 969, 617, 478 and 430 cm⁻¹. These properties indicate a close relation of the mineral to howieite. The mineral occurs as aggregates of needle-like crystals in cracks or as subordinate component in metamorphosed ferruginous chert belonging to glaucophane schist facies at the Taneyama mine, Kumamoto Prefecture, Southwestern Japan.