Virulundo is a nearly circular plug of carbonatite with a diameter of nearly 3 km, with which no consanguineous intrusive silicate rocks are associated. It forms a steep-sided, in places vertical, hill rising to 800 m above it's base. The plug intrudes granite gneisses and migmatites and an extensive area of dolerite cuts and overlies the granites to the east and south. The carbonatite comprises calcite, dolomite, ankerite, magnetite and secondary iron oxide minerals and is variably silicified. Other minerals identified include aegirine, barite, pyrochlore, apatite, fluorite, strontianite, zircon, hollandite and parisite/synchysite. A little malachite has been found and analyses indicate small tenors of Cu in most rocks. The carbonatite is surrounded by a collar of fenitized granitic rocks but the ruggedness of the terrane made contacts difficult to locate (Lapido-Loureiro, 1973). Much of the fenite is highly feldspathic and such rocks often occur as fragments set in a carbonatitic matrix. Chemical analyses (Lapido-Loureiro, 1973, Table 25) indicate that these rocks are potassic. A whole rock analysis of carbonatite (average of nine samples) is given by Issa et al. (1991) but individual samples represent calcio-, magnesio- and ferrocarbonatites.