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

Abstract

Taneyamalite (M.A. 81-1876) is triclinic, space group P1 or P1, with a 10.1882 + or - 0.0012, b 9.7544 + or - 0.0006, c 9.5674 + or - 0.0011 A, alpha 90.429 + or - 0.019o, beta 71.025 + or - 0.014o, gamma 109.168 + or - 0.007o, V 844.03 + or - 0.13 A3; Z = 1. Principal powder lines are 9.155(100), 3.252(37), 2.774(24), 7.948(22), 2.202(21) A. Wet chemical analysis gave 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, = 99.32%, corresponding with the ideal formula (Na,Ca)(Mn2+,Mg,Fe2+,Fe3+,Al)12(Si,Al)12(O,OH)44, where Na and Mn2+ are the dominant species in the respective sites. Taneyamalite is thus the Mn2+-dominant analogue of howieite. It is dark brown to black in colour, lustre vitreous, streak brown; good (010) and fair (100) cleavages; H. 5-6; sp. gr. 3.30 (meas.), 3.34 (calc. on unit-cell data) and 3.31 (calc. on Gladstone-Dale's law). It has 2Valpha approx 70o, alpha (pale golden yellow) 1.697, beta (yellowish brown) 1.720, gamma (dark brown) 1.732. The IR spectrum shows strong absorptions at 3525, 3420, 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 a subordinate component in metamorphosed ferruginous chert belonging to the glaucophane- schist facies at the Taneyama mine, SW Japan.-T.Y.