Chanja is located 12 km south of Balombo and forms a mountain rising 1650 m above the plain. The mountain is described as being composed of nepheline syenite, which forms the southern half of a four kilometre diameter ring structure, which is located at the intersection of two faults. However, other accounts describe this rock, or another in the area, as essexite (Lapido-Loureiro, 1967) or fayalite essexite (Andrade, 1954, analysis 8).
ANDRADE, M. de 1954. Contribution à l'étude des roches alcalines d'Angola (note preliminaire). 19th International Geological Congress, Algiers. Comptes Rendus, 19: 241-52.LAPIDO-LOUREIRO, F.E. 1967. Consideracoes sobre o quimismo dos sienitos nefelínicos. Breves referências a rochas alcalinas de Angola e ao seu interesse económico. Boletim do Instituto de Investigação Científica de Angola, 4: 37-65.MACHADO, F.J. de S. 1958. The volcanic belt of Angola and its carbonatites. Publication. Commission for Technical Cooperation in Africa South of the Sahara. Joint Meeting, Leopoldville, 44: 309-17.