The Lenderut Hills represent the remnants of a central volcano that predates the surrounding plateau trachytes (Baker, 1963b). The earliest rocks are identified as andesites by Baker consisting as they do of sparse phenocrysts of andesine, brown hornblende and pyroxene in a matrix of ‘intermediate’ or sodic plagioclase and tiny rods of pyroxene and abundant opaques. Rocks from the summit area are similar but contain a mineral tentatively identified as analcime. One described sample contains rare green pyroxene grains and small altered nephelines; they are classified as tephrites. The youngest rocks are described as porphyritic basanites and include labradorite, augite and olivine phenocrysts and abundant patches of analcime and ill-defined areas taken to represent an alkaline mesostasis.
BAKER, B.H. 1963b. Geology of the area south of Magadi. Report, Geological Survey of Kenya, 61: 1-27.FAIRHEAD, J.D., MITCHELL, J.G. and WILLIAMS, L.A.J. 1972. New K/Ar determinations on rift volcanics of S. Kenya and their bearing on age of rift faulting. Nature Physical Science, 238: 66-9.