What defines a sedimentary rock?

Sedimentary rocks are primarily defined by their formation process, which involves the accumulation and compression of sediments. These sediments can include eroded particles from pre-existing rocks, along with organic materials and mineral fragments. Over time, these materials settle in layers and may undergo lithification, a process that turns them into solid rock.

The correct response highlights that sedimentary rocks are formed from eroded particles, which can include fragments of other rocks, minerals, and even biological debris. This accumulation of sediments is what distinguishes sedimentary rocks from other types of rocks, such as igneous or metamorphic rocks that form through different processes.

Considering the other options illustrates the specificity of sedimentary rock formation. The option discussing molten material refers to igneous rocks, which form from cooled lava or magma. The choice regarding compressed organic matter aligns more closely with certain types of sedimentary rocks like coal, but it does not encompass the broader definition that includes all eroded particles. Lastly, a rock described as “changeable” does not accurately characterize sedimentary rocks, which are defined by their stable, layered structure after lithification.