Geographically, basalt is the foundation of the Earth’s oceanic basins. It forms at mid-oceanic ridges through the melting of the mantle. Because basaltic lava is very fluid (low viscosity), it can travel long distances, leading to the formation of broad, gently sloping shield volcanoes like those in Hawaii. Basalt is high in iron and magnesium, making it denser than the granitic rocks of the continents. This density difference is why oceanic crust sits lower than continental crust, forming the world’s ocean basins. On land, basaltic flows create fertile plains and massive “flood basalt” provinces.