<Original Papers>Mineralogical Study of Manganese Silicate Ores in Northeastern Japan.(XXVII) : Alleghanyite from Hanawa Mine, Iwate Prefecture

Alleghanyite occurs as aggregates of fine grained prismatic to anhedral crystals in the bedded manganese ore deposits of the Hanawa mine, in the highly metamorphosed Permian quatzite by the intrusion of the Miyako granitic mass. The mineral is associated closely with rhodochrosite. The mineral is brownish gray with vitreous luster. The specific gravity is 3.87 (measured); 3.91 (calculated). In thin section, it is colorless and biaxial negative with α=1.760,β=1.780,γ=1.790,2Vα=80°. Most of the crystals show lamellae twinning on (001) and the angle of extinction ((001) ΛX) is 24°. The mineral is monoclinic, space group P 2_1/b with a_0=4.86,b_0=10.75,c_0=8.27 A, α=108.73°and Z=2. Chemical analysis leads to an empirical formula (Mn_ Ca_ Mg_ Fe_ Al_)_ Si_ O_ (OH)_ F_, showing the mineral to be very close to theoretical Mn_5Si_2O_8 (OH, F)_2