Alkaline Rocks and Carbonatites of the World

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

Balombo And Nonga


Occurrence number: 
Longitude: 14.75, Latitude: -12.35

Andrade (1954) describes essexite, nepheline monzonite and nepheline syenite from the Balombo centre. The essexite and monzonite contain oligoclase-andesine with either sodic orthoclase or anorthoclase, the feldspars including nepheline and sodalite in graphic intergrowth, titaniferous augite, hornblende and biotite, which replace pyroxene, fayalite with rims of blue sodic amphibole, and accessories including cancrinite and zeolites. Three analyses are available (Andrade, 1954). Lapido-Loureiro (1967) records tinguaite from this area.It is not clear from the description of Andrade (1954) if Nonga is synonymous with Balombo or a different locality, but it is described in Andrade (1959) as northwest of Balombo. The rock described comprises 83% alkali feldspar, 10% aegirine, 5% analcime and a little aenigmatite and magnetite.

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.ANDRADE, M.M. de 1959. Analise quimicas de rochas eruptivas de Angola, publicadas áte fins de 1959. Publicações do Museu e Laboratorio Mineralógico e Geológico da Faculdade de Ciências do Porto, (4 Serie) 76: 1-77.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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