Basalt is an effusive rock of volcanic origin, dark or black color with a silica content. Basalt is mostly made up of calcic plagioclase and pyroxene; some basalts can also be rich in olivine. Basalt is the corresponding intrusive gabbro. Basalt may present with appearance ranging from porphyry to a glassy microcrystalline. It comes from a rapidly solidified magma in contact with air or water and is the main constituent rock the upper part of the oceanic crust. The basaltic magmas are formed by decompression melting of the mantle.