One of two primary categories of igneous rocks classified quantitatively by their chemical composition: see femic, adj. Contrasted with sal (sal, n.4…

One of the two primary categories erected by Cross, Iddings, Pirsson, and Washington to classify igneous rocks and their characteristic minerals…

Of an igneous rock: composed chiefly of mafic minerals. Also as n.

Of an igneous rock: having a silica content that is lower than that of the basic rocks (cf. basic, adj. 2b), spec. less than 45 per cent by…

An ultramafic extrusive rock notably rich in magnesium, often with a characteristic spinifex texture.