Definition of ultramafic

1. Igneous rocks that contain more than 90 vol-% mafic minerals are called ultramafic. These rocks are classified by their relative content of olivine, orthopyroxenes and clinopyroxenes.
(IUGS recommendation for the classification of igneous rocks)



2. Said of an igneous rock composed chiefly of mafic minerals, e.g., monomineralic rocks composed of enstatite, augite, or olivine.

Compare with: hypermelanic, ultrabasic

Ref: AGI