Elemental abundances in ultramafic rock and their relation to the upper mantle

Neutron activation and spectrographic data on 58 ultramafic rocks, representative of diverse geographic and geologic settings, indicate considerable differences in abundances of Al, Si, Ti, Co, Cr, Fe, Sc, Mn, Cu, V, and Ni. These wide differences in composition vitiate any calculation of mean elemental abundances for ultramafic rocks taken as a single homogeneous group and indicate gross chemical differentiations either within the mantle or between the mantle and the ultramafic rocks.