Le Bas and Mohr (1968) describe melanephelinite and tinguaite, collected by Sowerbutts, from immediately north of the Batu Mountains. On the 1:2,000,000 geological map (Merla et al., 1979) Batu is shown as a large (60x40 km) volcanic centre. The rock is an olivine melanephelinite which contains olivine and augite phenocrysts set in a groundmass of colourless to pale green pyroxene, fresh euhedral nepheline, an opaque phase and interstitial analcime. The tinguaite contains alkali feldspar phenocrysts and microphenocrysts of nepheline in a trachytic groundmass of orthoclase, aegirine-augite zoned to aegirine and a little apatite.
LE BAS, M.J. and MOHR, P.A. 1968. Feldspathoidal rocks from the Cainozoic volcanic province of Ethiopia. Geologischer Rundschau, 58: 273-80.MERLA, G., ABBATE, E., AZZAROLI, A., BRUNI, P., CANUTI, P., FAZZUOLI, M., SAGRI, M. and TACCONI, P. 1979. A geological map of Ethiopia and Somalia (1973) 1:2,000,000 and comment with a map of major landforms. Consiglio Nazionale delle Ricerche Italy. Centro Stampa, Firenze. 1-95.