Most common volcanic rock

Basalt accounts for more than 90% of all volcanic rock at the Earth’s surface. It is the biggest component of the oceanic crust and is also the main rock type seen in many of the Earth’s mid-ocean islands, including the Hawaiian islands and Iceland. It is fine-grained in texture and dark in colour, with around 50% silica and high percentages of iron and magnesium.

It also occurs as flood basalts on Earth’s continental crust, where its low viscosity allows it to flow over significant distances. Flood basalts make up the dark areas (maria) of the surface of the Moon.