Sedimentary
Contents
Key Stage 3
Meaning
A sedimentary rock is one made from layers of sediment that have been deposited at the bottom of a river, lake or sea bed.
About Sedimentary Rocks
- Sedimentary rocks are usually soft compared to other rocks.
- They are made of rounded grains held together by mineral salts.
Formation of Sedimentary Rocks
- Weathering - Rocks are broken down by the environment.
- Erosion - Wearing away rocks into smaller pieces.
- Transport - Small pieces of rock are moved by rivers, glaciers and the wind.
- Deposition - When water and the wind slow down or when glaciers melt the small pieces of rock fall to the ground.
- Sedimentation - Layers of sediment (small pieces of rock) build up on lake beds and sea beds.
- Compaction - So many layers build up that the pressure squeezes all the water out.
- Cementation - Mineral salts that were dissolved in the water fall out of solution and bind the sediment together.
Examples
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| Mudstone is formed from mud. | Limestone is formed from the shells of dead sea creatures. | Sandstone is formed from rounded grains of sand. |