diabase

n. [ F. diabase, fr. Gr. &unr_; a crossing or passing over, fr. &unr_;; &unr_; + &unr_; to go; -- so called by Brongniart, because it passes over to diorite. ] (Min.) A basic, dark-colored, holocrystalline, igneous rock, consisting essentially of a triclinic feldspar and pyroxene with magnetic iron; -- often limited to rocks pretertiary in age. It includes part of what was early called greenstone. [ 1913 Webster ]