The majority of the mountain lies in Engaruka Ward, and a quarter of it is in the Ngorongoro Conservation Area.

[2] Kerimasi, an extinct nephelinite volcano in northern Tanzania's eastern rift valley, emitted carbonatite tephra during its final eruptive phase.

The tephra was primarily composed of alkali carbonatite, making it the earliest well-documented example of premodern natrocarbonatite volcanism.

The main carbonate mineral was nyerereite, which is also the major mineral in present natrocarbonatite lava flows from the neighboring volcano Oldoinyo Lengai.

Kerimasi's nyerereite was leached of its alkalis by meteoric water, and it is currently represented by calcite pseudomorphs.