What is the primary composition of a dune?

Dunes are primarily composed of well-sorted fine to medium sand due to their formation process, which primarily occurs in arid or semi-arid environments. The wind moves and deposits sand particles over time, resulting in the characteristic shape of the dune. The sorting process means that the sand grains tend to be similar in size, which contributes to the stability and formation of the dune structures. Fine to medium sand is particularly adept at being transported by the wind, making it the dominant material in dune formations. Other soil compositions, such as clay, silt, or organic-rich material, do not play a significant role in the structure of dunes, which is why the correct choice highlights the importance of sand in their development.