Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Chapeu Armado


Occurrence number: 
Longitude: 12.35, Latitude: -14.47

Dykes which occur in the vicinity of Chapeu Armado, one of which forms the summit of Chapeu Armado Hill, are nephelinites (Beetz, 1934). They consist of phenocrysts of titanaugite set in a matrix of nepheline with needles of aegirine-augite; olivine occurs in some rocks and analcime and apatite are accessory. Andrade (1957) gives a rock analysis, which indicates 14% normative orthoclase.


ANDRADE, M.M. de 1957. Rochas vulcânicas da orla mesocenozóica entre Benguela e Moçâmedes. Garcia de Orta. Revista da Junta de Investigações do Ultramar, 5: 739-68.BEETZ, P.F.W. 1934. Geology of south west Angola, between Cunene and Lunda Axis. Transactions of the Geological Society of South Africa, 36: 137-76.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.

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