ultramafic

== English == === Etymology === From ultra- +‎ mafic. === Adjective === ultramafic (comparative more ultramafic, superlative most ultramafic) (geology) Describing igneous rocks that contain magnesium and iron and only a very small amount of silica, such as are found in the Earth’s mantle. ==== Synonyms ==== ultrabasic === Noun === ultramafic (plural ultramafics) A rock with such properties.