Abstract
The new mineral, nambulite, is a lithium- and sodium-bearing hydrous manganosilicate discovered at the Funakozawa manganese mine in the Kitakami mountains, northeastern Japan. Coarse prismatic crystals of the mineral occur in the veinlets in the braunite ore. It has vitreous reddish brown color with orange tint; and perfect (001), distinct (100) and (010) cleavages. Mohs' hardness is 6.5. Specific gravity is 3.51±0.01 (meas.) and 3.49 (calc.). Optically it is biaxial positive with refractive indices (Na-light) α=1.707, β=1.710, γ=1.730 (all±0.002); with 2V=30° ±2° and X'∧c=19°.
Chemical analysis gives: SiO2 49.23, TiO2 0.01, Al2O3 0.37, Fe2O3 0.40, MnO 40.67, MgO 1.32, CaO 0.81, Na2O 2.49, K2O 0.04, P2O5 0.02, Li2O 1.55, H2O+ 1.63, H2O- 0.26, CO2 0.19, total 98.99%. The result yields the formula Li1.00(Na0.98K0.01) (Mn6.95Mg0.40Li0.27Ca0.18Al0.09Fe+30.06) Si10.00O27.79(OH)2.21, which may be written ideally as LiNaMn8Si10O28(OH)2.
It is triclinic and the crystallographic data are as follows: space group, P1 or P ?? ; a=7.621, b=11.761, c=6.731Å (all ±0.003Å); α=92°46', β=95°05', γ=106°52' (all ±3'); V=573.4±0.3Å3; Z=1. Principal powder lines (d in Å) with relative intensities and indices are: 7.11 (25) ( ?? 10), 6.70 (25) (001), 3.56 (20) ( ?? 20), 3.54 (35) (12 ?? ), 3.34 (40) (1 ?? 1, 002, ?? 01), 3.17 (65) ( ?? 02, 031), 3.14 (45) (012), 3.09 (55) ( ?? 12), 3.07 (60) (2 ?? 1), 3.01 (30) (11 ?? ), 2, 97 (80) (0 ?? 2), 2.96 (100) (1 ?? 2), 2.92(70) ( ?? 40, 102), 2.71 (35) (112, 220). Infrared spectrum shows strong absorptions at 1040, 935, 890 and 460 cm-1.
Nambulite may be an alkaline analogue of rhodonite.
The mineral name is for Professor Matsuo Nambu of Tohoku University.
