Natronambulite, (Na, Li)(Mn, Ca)₄Si₅O₁₄OH, a new mineral from the Tanohata mine, Iwate Prefecture, Japan

Abstract

Natronambulite, (Na, Li)(Mn, Ca)₄Si₅O₁₄OH(Na > Li; Mn > Ca) is triclinic, P1 or P-1, a = 7.620, b = 11.762, c = 6.737Å, α = 92.81°, β = 94.55°, γ = 106.87°, Z = 2. The electron microporbe and wet chemical analyses gave SiO₂ 50.39, TiO₂ 0.03, FeO 0.31, MnO 38.94, MgO 1.24, CaO 3.66, Na₂O 3.55, Li₂O 0.43, H₂O⁺ 1.46, H₂O⁻ 0.54, total 100.55%, yielding the empirical formula (Na_0.69Li_0.17)Σ_0.86(Mn_3.32Ca_0.39Mg_0.19 Fe_0.03)Σ_3.93Si_5.07O_14.02(OH)_0.98 (basis O = 15), or ideally (Na, Li)(Mn, Ca)₄Si₅O₁₄OH (Na >Li; Mn > Ca).
It is pinkish orange in colour with a vitreous luster and nearly white streak. H.(Mohs) = 5^1⁄2−6. Density (g/cm³) 3.51 (meas.), 3.50 (calc. using the empirical formula). Cleavage [100] and [100], perfect. Optically it is biaxial and positive, 2V ≈ 45°, r > v, moderate. Refractive indices are: α = 1.706(2), β = 1.710(2), γ = 1.730(5). It is nearly colourless in thin section.
It occurs in a low grade manganese ore from the thermally metamorphosed manganese ore deposit of the Tanohata mine, Iwate Prefecture, Japan, in association with manganoan aegirine, manganoan arfvedsonite, quartz and rhodonite, or with albite, microcline, quartz and serandite.