Sedimentary rocks are formed by the deposition of mud, clay, sand and other small particles on the surface of the Earth. Sedimentation can occur in many different environments, including lakes, rivers, deserts and oceans. The sediment is deposited in layers that are compressed over time and turned into solid rock.
The most common types of sedimentary rocks are made from quartz or clay that is eroded and carried away by wind or water. These small particles are then deposited in a different part of the Earth. Over time, as these layers of deposition are buried and compressed, the heat and pressure fuse them together to form layers of solid rock, such as sandstone or shale.
Sedimentary rocks can also be formed from the remains of marine invertebrates, such as plankton and other small organisms. Their shells are made out of calcium carbonate. When they die, their remains sink slowly to the bottom of the ocean, forming thick layers that become limestone or chert.
Evaporating minerals from the ocean can also lead to the formation of sedimentary rocks. As shallow seas evaporate, layers of calcite, gypsum and halite settle out of solution. Over time, if these layers are left undisturbed, they can be turned into rocks known as evaporites.