The Probert Encyclopaedia of Rocks & Minerals

DIABASE

Diabase is a dark, intrusive, basic igneous rock made up of plagioclase feldspar crystals, surrounded by smaller grains of pyroxenes, such as augite and up to ten percent quartz. Diabase is formed from magna that has cooled just below the Earth's surface, and is sometimes found as intrusions in older rock. A common place to find diabase is in the neck of old volcanoes, where it has formed a plug.
Research Diabase