Abstract
Five pairs of biotite and hornblende from the rocks of the Senmaya granitic intrusion in the southern Kitakami Mountains were analysed chemically. The apparent distribution coefficient of Mg-Fe2+ between biotite and hornblende is considerably controlled by the My/Fe2+ ratio as well as the AlIV content of hornblende in calc-alkaline granitic rocks from Senmaya district and other various localities in the world.
With regard to the chemistry of hornblende coexisting with biotite in granitic rocks, the following facts are established: The relation between the Mg/Fe2+ ratio and any one of the AlIV, (Na+K), (AlVI+Fe3+) and Ti contents shows a good linearlity with a negative gradient; the difference in magnitude between the AlIV and (Na+K+AlVI+Fe3++Ti) contents is ascribed to the effects of the glaucophane-riebeckite and/or richterite substitutions.
