Basalt is a volcanic rock (microlitic structure).
From a primary magma from partial melting of the mantle peridotites.
The rocks are classified as basic as base-rich (MgO, FeO) and low alkali (K2O, Na2O).
They are dark because of Fe2O3.
Ridges produce MORB basalts (Medio Ocean Ridge basalts)
These basalts are characterized by their small amount of alkali (Na20 and K2O), as well as a small amount of silica SiO2, as shown in the diagram straight out of the geochemistry laboratory.