- a fine-grained gabbro occurring as minor intrusions.
- British. a dark igneous rock consisting essentially of augite and feldspar; an altered dolerite.
- British an altered dolerite
- US another name for dolerite
- A dark-gray to black, medium-grained igneous rock consisting mainly of labradorite and pyroxene. Diabase is compositionally similar to andesite, but has coarser grains. It is commonly found in sills and dikes. Also called dolerite