What defines sedimentary rock?

Sedimentary rock is defined by the process of formation involving the accumulation, compacting, and cementing of sediment. This sediment originates from the erosion and weathering of pre-existing rocks, minerals, and organic materials, which may then be deposited in layers over time. As these layers build up, the weight of the overlying materials exerts pressure, causing the particles to fuse together through a combination of compaction and natural cementation, often involving minerals like calcite or silica.

This definition highlights that sedimentary rocks are the result of a specific formation process, which distinguishes them from other rock types. For example, igneous rocks form from the cooling and solidification of magma or lava, while metamorphic rocks arise from the alteration of existing rocks due to heat, pressure, or chemically active fluids. Understanding these processes helps clarify why the characteristics attributed to sedimentary rocks, particularly the pressing and cementing of sediments, are central to their definition.