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.