Sedimentary rocks come from the fragments of pre-existing rocks called sediments. There are three types of sedimentary rocks, each coming from different kinds of sediments. Clastic sedimentary rocks are created from the broken pieces of other rocks, while chemical sedimentary rocks form from mineral crystals like halite and gypsum.
Organic sedimentary rocks are formed from the remains of living things, such as plants, dinosaur bones, plankton skeletons and clamshells. These rocks preserve fossils of ancient living things. Sediments form a rock when the tiny pieces become cemented together. Sedimentary rocks compose three-quarters of the rocks on Earth's surface. They form in various places including rivers, oceans, beaches and any environment where sediments, like sand and mud, collect.
Weathering causes pre-existing rocks to break up into pieces. When the rocks are weathered and disintegrated into sediments, wind, water, gravity or glaciers transport them to various depositional environments. Once the sediments become deposited, they accumulate and form a sedimentary rock via lithification, which occurs through compaction, cementation or crystallization.
Sedimentary rocks are made up of carbonates, clay minerals, silica, evaporites, organic matter, heavy minerals, feldspar and rock particles. The sedimentary structures, particle size, composition and texture are the properties used to identify the type of sedimentary rock and its depositional environment where it was formed.