Nickel and cobalt minerals of the Tiyo-ga-hara mine are contained in small veins, cutting diorite-porphyrite near its contact with Triassic sandstone. They are accompanied by some chalcopyrite and pyrrhotite, the latter of which has mostly altered into marcasitic aggre-gates due to later solutions. The cobalt mineral occurs as small well-defined crystals bounded by cubic and octahedral faces, o ?? ten with those of pentagonal dodecahedrons. It contains, besides cobalt, iron, arsenic and sulphur. The result of chemical analysis, made by J. Kitahara, gives its composition as follows:
Co 15.31, Fe 22.25, As 39.52, S. 22.56%
Thus it seems to belong to “ferro-cobaltite”, the existence of which has been doubted. Its polished surface shows, under micrcscope, characteristics of cobaltite, except that the reddish tint of the colour is obscure. Nickel mineral is identified as gersdorffite, which is usually xenomorphic, being replaced and traversed by irregular veinlets of surrounding chalcopyrite.