The basaltic rock that forms volcanic mountains where the mantle plumes reach the Earth's surface is usually composed of fine-grained, dark-colored felsic materials. Basalt is a hard, black rock which is formed when magma or lava from volcanic eruptions cools down and hardens. It consists of fine mineral grains. It can also consist of holes that were filled by volcanic gases. Basalt is black because the minerals that it is made up of contains iron. Iron gives basalt its black colour.
