Small pieces of rock are called sediment, although sediment is found in a wide range of sizes. Sediment is created from the weathering and erosion of large rocks, as well as from other natural and unnatural processes.
Regardless of their size, all pieces of rock that break off of other rocks are called sediment. Wind, water and gravity are the primary causes of rocks breaking off into smaller pieces and being moved around. Sediment can travel short or long distances depending on what led to the initial movement, and this movement can cause even further erosion to the rock. When the sediment is no longer transported, it collects with other sediment to form piles of rocks or sand.