Which type of rock is often formed from the accumulation of organic materials and sediments?

The type of rock formed from the accumulation of organic materials and sediments is sedimentary rock. These rocks are typically created through processes such as the compaction and cementation of particles, including fragments of other rocks, mineral grains, and organic materials like plant and animal remains. Over time, layers of these materials build up, and the pressure from the layers above helps to solidify them into rock.

Sedimentary rocks can often be found in environments such as riverbeds, lakes, and ocean floors where sediment can accumulate. They commonly feature recognizable layering and may also contain fossils, providing valuable information about the Earth's history and past life. This process of formation distinguishes sedimentary rock from the other types mentioned, such as metamorphic, which is formed under heat and pressure from existing rock, igneous, formed by the cooling and solidification of molten rock, and crystalline rock, which is generally associated with a specific texture or mineral composition but does not specifically relate to organic accumulation or sediment deposition.