Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earths surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. Sedimentary rocks are formed when sediment is deposited out of air, ice, wind, gravity, or water flows carrying the particles in suspension. This sediment is often formed when weathering and erosion break down a rock into loose material in a source area. The material is then transported from the source area to the deposition area. The type of sediment transported depends on the geology of the hinterland (the source area of the sediment) .

Most sedimentary rocks contain either quartz (siliciclastic rocks) or calcite (carbonate rocks) . In contrast to igneous and metamorphic rocks, a sedimentary rock usually contains very few different major minerals. However, the origin of the minerals in a sedimentary rock is often more complex than in an igneous rock. Minerals in a sedimentary rock may have been present in the original sediments or may have formed by precipitation during diagenesis.

Sedimentary rocks are laid down in layers called beds or strata. A bed is defined as a layer of rock that has a uniform lithology and texture. Beds form by the deposition of layers of sediment on top of each other. The sequence of beds that characterizes sedimentary rocks is called bedding. Single beds can be a couple of centimeters to several meters thick. Finer, less pronounced layers are called laminae.

There are three basic types of sedimentary rocks: clastic, chemical, and organic. Clastic sedimentary rocks are made up of pieces (clasts) of pre-existing rocks loosened by weathering. These rocks have particles ranging in size from microscopic clay to huge boulders. Chemical sedimentary rocks form by chemical precipitation that begins when water traveling through rock dissolves some of the minerals. These minerals are carried away from their source and eventually redeposited, or precipitated, when the water evaporates away. Organic sedimentary rocks form from the accumulation of plant or animal debris.

In summary, sedimentary rocks are formed by the accumulation or deposition of mineral or organic particles at Earths surface, followed by cementation. They are laid down in layers called beds or strata and are classified into three groups: clastic, chemical, and organic.