Here's why:
* Basalt is a dark-colored, fine-grained volcanic rock that is rich in magnesium and iron.
* The oceanic crust is primarily formed by volcanic activity at mid-ocean ridges, where magma rises from the mantle and cools to form new crust.
* This magma is typically basaltic in composition, and the resulting oceanic crust therefore shares similar characteristics.
While the oceanic crust is not entirely composed of basalt, it is the dominant rock type. Other components include:
* Gabbro: A coarse-grained intrusive igneous rock, similar in composition to basalt.
* Diabase: A medium-grained intrusive igneous rock, also similar to basalt.
* Serpentinite: A metamorphic rock formed from the alteration of ultramafic rocks like peridotite.
However, basalt remains the best approximation for the average composition of the oceanic crust.
