Basalt.
Igneous Rock
Crust under the oceans is called oceanic crust.
The surface of the Earth is called the "crust" which is geological terms is the outermost layer of planet or satellite. In the case of the Earth, the crust is composed of igneous, metamorphic and sedimentary rocks and is about 20miles to 50miles thick on the continent and about 3 to 6miles thick in the ocean.
oceanic crust
The crust beneath the ocean is called oceanic crust. It is thinner and younger than continental crust, primarily composed of basaltic rock formed at mid-ocean ridges through volcanic activity.
It is mostly composed of basalt, and few other mineral types. It is made mostly of igneous rock, same with continental crust.
Basalt
The crust not under the ocean is called continental crust. It is thicker and less dense compared to oceanic crust and forms the landmasses on Earth's surface.
continental crust
The color of the rock that forms oceanic crust at mid-ocean ridges is dark gray to black. The rock is primarily basalt, which is a type of igneous rock formed from the solidification of molten lava.
Basalt is the igneous rock which makes up most of the ocean floors. It is smooth and velvety-black in appearance and very hard. New seafloor is constantly produced at the mid-ocean rifts, where areas between spreading tectonic plates are infilled with rapidly cooling lava.
It is found at the bottom of the ocean!