Diabase
Diabase, an igneous rock similar to basalt in composition, but with coarser grains. Diabase generally forms dikes; that is, it fills fissures or cracks in some other rock. It is found in most parts of the world.

Diabase, an igneous rock similar to basalt in composition, but with coarser grains. Diabase generally forms dikes; that is, it fills fissures or cracks in some other rock. It is found in most parts of the world.