Granite petrology has achieved significant progress since Tuttle and Bowen (1958) wrote the monograph on the Origin of granite in the light of experimental studies in the system NaAISi308-KAISi308-SiOrH20. Since then, the components CaAI2Si20 s, FeO, MgO, and excess alumina have been added to the pure system Ab-Or-Qz-H20 in order to include plagioclase and common mafic minerals in the investigations.