Diabase \Di"a*base\, n. [F. diabase, fr. Gr. ? a crossing or
passing over, fr. ?; ? + ? 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]