*dolerite*

n. [ Gr. dolero`s deceptive, because it was easily confounded with diorite. ] (Petrography) (a) A dark, crystalline, igneous rock, chiefly pyroxene with labradorite. (b) Coarse-grained basalt. (c) Diabase. (d) Any dark, igneous rock composed chiefly of silicates of iron and magnesium with some feldspar. -- Dol`er*it"ic a. [Webster 1913 Suppl.]