Basalt
Basalt  is a common grey to black rock. It is pushed out (extruded) by volcanos. The lava is rich in magnesium and iron. It has olivine and pyroxene minerals which make it dark in colour. Basalt is usually fine-grained because the lava cools rapidly on the Earth's surface. Flood basalts are commonplace, formed by lava pouring out and solidifying.