Coexisting biotites and hornblendes in granitic rocks from the Kitakami mountains were chemically analyzed. Most of biotites have composition near the phlogopite-annite series. Hornblendes of the Hitokabe, Tono and Kesengawa masses are similar in composi-tion one another, but those of the Hirota mass are poorer in Al and Na+K and richer in Si than those of the former three masses. The Mg-Fe
+2 distribution coefficients for coexisting biotite-hornblende pairs from the Hitokabe, Tono, Kesengawa and Hirota masses are 0.79, 0.69, 0.70 and 0.67, respectively. These differences depend largely upon Al contents in these minerals.
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