Part of Hall of Planet Earth.
Sedimentary rocks are layered. Some form when particles of rocks and minerals settle out of water or air. Others form when minerals precipitate directly out of water. Sedimentary rocks are identified by their minerals and texture.
As the sediments pile up, water is driven out by the weight of the overlying pile, and minerals precipitate around the sediment particles, cementing them into rock. This process is called lithification.