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What is sedimentary rock?
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Quick answer
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.
Key things to understand
- It forms from sediment (sand, silt, mud, shell fragments) that settles, compacts, and cements over time.
- It usually forms in flat layers, called strata, often visible as bands in cliffs.
- Most fossils are found in sedimentary rock, because remains get buried in the soft layers.
- Examples: sandstone, limestone, shale, and chalk.
- It can later be changed into metamorphic rock by heat and pressure.
People also ask
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.
Part of the guide: Nature & Earth: Living Things and Rocks →