An elliptical multiple intrusion 31x12 km and covering 330 km2, Itatiaia is emplaced in Precambrian gneisses, but at the southeastern end is in poorly defined contact with Tertiary clastic sediments. Within the intrusion there is a gradual transition from nepheline syenites and/or sodalite syenites into pulaskites, quartz syenites and nordmarkites and finally into peralkaline granites. Foyaite and pseudoleucite tinguaite occur and microsyenite and tinguaite dykes cut the pluton and adjacent country rocks. Magmatic breccias form two large bodies in the northern part of the intrusion and grade into the surrounding rocks. They comprise fragments of phonolitic and trachytic rocks in a matrix of similar composition. A vein a few cm wide and rich in REE, Sr and Th was described by Mau and Coutinho (1959) for which a carbonatitic association was suggested on the grounds of chemistry and mineralogy, including the presence of some calcite.