The 35x20 km Zinder occurrence is partly masked by Cretaceous sediments. It consists of biotite, riebeckite and arfvedsonite granites, microgranites and rhyolites with a small isolated intrusion of alkaline syenite lying 6 km to the east. Coarse granites, with microcline perthite crystals 5-10 mm in diameter, are the most abundant rocks. They contain either riebeckite or arfvedsonite with aegirine occurring sporadically. The biotite granite, which is less extensive, contains riebeckite as well as biotite. Both sodic amphiboles and biotite are found in the microgranites.