What is the primary composition of the Earth's crust?

The primary composition of the Earth's crust is indeed granite and basalt. The Earth's crust is the outermost layer, and it is predominantly made up of these two types of igneous rocks. Granite is a light-colored, coarse-grained rock that mostly comprises quartz and feldspar, while basalt is a dark-colored, fine-grained rock that is rich in iron and magnesium.

In continental regions, granite is more prevalent, forming the bulk of the continental crust, whereas basalt typically forms the oceanic crust, which is denser and thinner. This composition of granite and basalt reflects the diverse geological processes that form the Earth's surface, including volcanic activity and tectonic movements.

Silica and aluminum, while they are key components of the minerals found in granite and other crustal materials, do not represent the primary composition in terms of the rock types themselves. Iron and nickel are mostly found in the Earth's core rather than the crust. Calcium and magnesium are elements found in some minerals within the crust but are not the main rock types that define it. Thus, granite and basalt accurately represent the dominant rock types that make up the Earth's crust.