Sand dunes make up only about 15 percent of the Sahara, but the desert is so huge (about three and a half million square miles or 5.63 million sq km) that even a single dune may be enormous. The sand dune known as the Libyan Erg is as big as France.

About 70 percent of the Sahara consists of rocky plains covered with stones and gravel. Shale and limestone plateaus or mountain ranges make up the rest.