What type of rock forms when sediment collects and hardens?

Sedimentary rocks form through the accumulation and compaction of sediment, which includes particles like sand, silt, clay, and fragments of other rocks. Over time, these sediments are compressed by the weight of overlying materials and undergo lithification, a process that transforms loose sediment into solid rock. This type of rock formation primarily occurs in layers, often found in environments such as riverbeds, lakebeds, and ocean floors, where sediment can gather over time.

The key characteristic of sedimentary rocks is their formation from pre-existing materials, making them distinct from other rock types. Unlike igneous rocks, which form from the cooling and solidification of molten material, or metamorphic rocks, which are created when existing rocks undergo changes due to heat and pressure, sedimentary rocks represent a unique process of sediment accumulation. Thus, the correct identification of sedimentary rocks highlights the geological cycle involved in rock formation and the importance of sediment in the Earth's system.