What are the two main types of crust?

Earth’s crust is divided into two main types. They are the oceanic crust and the continental crust.

• Oceanic crust: Oceanic crust extends 5-10 kilometres beneath the ocean floor. It is mostly composed of different types of basalts. Geologists often refer to the rocks of the oceanic crust as sima. Sima stands for silicate and magnesium, the most abundant minerals in oceanic crust.
• Continental crust: Continental crust is mostly composed of different types of granites. Geologists often refer to the rocks of the continental crust as sial. Sial stands for silicate and aluminium, the most abundant minerals in the continental crust. 

Continental crust is almost always much older than oceanic crust. Because continental crust is rarely destroyed and recycled in the process of subduction

Further Reading:

• Geomorphic Processes
• The Origin And The Evolution Of The Earth