Abstract
The manganese ore, locally called “Kimiman” or “Kibiman” by the miners at the Noda-Tamagawa mine, is composed essentially of pyrochroite ?? Mn(OH)2 ?? hitherto known as a rare mineral. More than 50, 000 tons of the pyrochroite ore have been shipped from this mine for metallurgical uses since 1950. The ore consists mainly of fibrous pyrochroite pseudomorph after manganosite with small amounts of manganosite, galaxite, tephroite, rhodochrosite, barite and alabandite. The pyrochroite occurs in scaly aggregates. When fresh, it is white but when exposed in air its colour changes into brown to black. Extinction is parallel to the elongated fiber. Character of zone is positive, ε=1.683, ω=1.725 and ω-ε=0.042. The unit cell dimensions obtained from the powder data: a0=3.323Å. and c0=4.738Å. The pyrochroite ore is considered to be hydrothermal alteration product from the manganosite ore, which may have been formed as dissociation product from the rhodochrosite ore of sedimentary type during the period of contact metamorphism of granitic intrusion.
