Constituent minerals such as amphibole, biotite, pyroxene, feldspar, magnetite, ilmenite, and others among the 25 representative rocks from the Tokuwa batholith were analyzed by electron microprobe following the procedure described by Nakamura and Kushiro (1970). The textural and compositional features of these minerals will be reported in this chapter in order to characterize the differences between magnetite-series and ilmeniteseries rocks.