Final answer:
Basalt is the dark, black volcanic rock that composes the oceanic crust, formed by cooling lava and comprising elements such as silicon and oxygen.
Step-by-step explanation:
The dark, black volcanic rock that makes up the oceanic crust is basalt. This type of igneous rock is produced by the cooling of lava. The oceanic crust is largely composed of basaltic rock, which is formed when mafic magma cools and erupts on the seafloor. Its composition includes elements such as silicon, oxygen, iron, aluminum, and magnesium. Unlike granite, which primarily makes up the continental crust, basalt is associated with the oceanic crust and covers most of Earth's surface that lies submerged under the oceans. Basalt's properties and formation make it one of the most prevalent rocks on Earth and even on other planetary bodies such as the Moon.