What are cays primarily composed of?

Cays are primarily composed of sand and coral because they are typically formed from the accumulation of sand deposited by ocean currents and the growth of coral reefs. These coral reefs provide the base structure upon which sand can build up over time, often resulting in a low-lying, sandy island surrounded by water. This natural process makes sandy cays common in tropical and subtropical regions, particularly in areas adjacent to coral reef systems. The presence of living coral also contributes to the ecological diversity of cays, fostering unique habitats for various marine species. The other options do not correspond with the geological makeup of cays; mountain and rock formations, ice and snow, or clay and silt are not typical components that define these landforms.