Hornblendes of some Ryoke granites were analysed chemically. Most of them are rich in iron and aluminum and some of them in alkalies. These characteristics are quite different from those of the Kitakami Mountains, Northeast Japan, which are relatively poor in iron and aluminum. Iron ores in the Ryoke granites are ilmenite and pyrrhotite (Tsusue & Ishihara, 1974), whereas those in the Kitakami granites are generally magnetite.
These differences between granites from the two districts reflect the difference of oxygen fugacities during crystallization of granitic magmas. In the Ryoke Belt, oxygen fugacities were considerably lower than those in the Kitakami Mountains.