This stock-like intrusion of 12 km2 is composed predominantly of medium-grained porphyritic peralkaline granites which cut porphyritic peralkaline syenites and quartz syenite porphyries. The associated dykes are of peralkaline granite porphyry. The rock-forming minerals are anorthoclase, albite, quartz, hastingsite, arfvedsonite and aegirine. Autometamorphism is manifested by the development of albite and fluorite, sometimes by kaolin and by a greisenization. Accessory minerals are zircon, ilmenite, apatite, fluorite, garnet, monazite, anatase, titanite and fluorite.