Here's a breakdown:

* Oceanic crust is primarily composed of basalt and gabbro, which are mafic igneous rocks.

* Mafic rocks are characterized by a high content of magnesium (Mg) and iron (Fe), along with silica (SiO2).

* Silica is the primary component of these rocks, typically making up around 45-55% of their weight.

Note: The exact silica content can vary slightly depending on the specific location and geological processes involved in the formation of the oceanic crust.