Resource Dictionary


Dark-colored, silica-poor volcanic rock composed primarily of plagioclase and pyroxene, sometimes with olivine and quartz. Produced at ocean island volcanoes such as Hawaii’s Kilauea, and various locations on the continents. Massive outpourings of basalt, known as flood basalts, have occurred periodically throughout geologic time, producing features such as the Deccan Traps in India and the Columbia Plateau in the northwestern U.S. Basalt horizons occasionally host economic deposits of gold, copper, chromite, and other metals.