This bit is worth remembering:- BIG CRYSTALS COOLED SLOWLY UNDERGROUND INTRUSIVE SMALL CRYSTALS COOLED QUICKLY AFTER AN ERUPTION EXTRUSIVE COMMON IGNEOUS ROCKS Basalt This is the most common form igneous rock which makes up most of the ocean floors.
(igneous rock; makes up; most of the ocean floors)
igneous rock
makes up
most of the ocean floors