Science
What is Sedimentary Rock?
Sedimentary rock forms when layers of sediment — bits of sand, mud, shells, and other material — pile up and are compressed and cemented together over long periods. It's one of the three main rock types, and it's where most fossils are found.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains sedimentary rock.
Key things to understand
- 1It forms from sediment (sand, silt, mud, shell fragments) that settles, compacts, and cements over time.
- 2It usually forms in flat layers, called strata, often visible as bands in cliffs.
- 3Most fossils are found in sedimentary rock, because remains get buried in the soft layers.
- 4Examples: sandstone, limestone, shale, and chalk.
- 5It can later be changed into metamorphic rock by heat and pressure.
Frequently asked questions
- How does sedimentary rock form?
- Sediment — broken-down rock, sand, mud, and shells — settles in layers, then the weight above compacts it and natural cements bind it into solid rock over thousands to millions of years.
- Why are fossils found in sedimentary rock?
- Because plants and animals get buried gently in soft sediment layers, which harden around them — preserving their shape. Igneous and metamorphic rock form in ways too hot or violent to keep fossils.
- What are examples of sedimentary rock?
- Sandstone (from sand), limestone (often from shells), shale (from mud), and chalk. Their layers are often visible in cliffs and canyons.