Komatiite.

It is easy to explain roughly what a komatiite is but difficult to give a rigorous definition. The simple definition is that komatiite is an ultramafic volcanic rock (Arndt and Nisbet 1982). Alimit of 18% MgO separates komatiites from less magnesian volcanic rocks such as picrites,ankaramites or magnesian basalts. The term komatiitic basalt is applied to volcanic rocks containing less than 18% MgO that can be linked, using petrological, textural or geochemicalarguments, to komatiites