Sedimentary rocks are formed from sediment grains deposited by water, wind or ice. They are always formed in layers, called “beds” or “strata”, and quite often contain fossils.
- Conglomerate is made up of rounded pebbles (>2mm) cemented together.
- They are formed from sediment deposited by fast-flowing rivers or by waves on beaches.
- Mudstone is made up of fine-grained clay particles (<0.05mm) compressed together.
- Mudstones form where clay has settled out in calm water – in lakes, lagoons, or deep sea.
- Flaky mudstone is called shale.
- Sandstone is made of sand grains (0.05-2mm) cemented together.
- It is formed from sediment deposited by rivers, the sea, or by the wind, so there are many types of sandstone.
Limestone & Chalk
- Limestone is made up of calcium carbonate (fizzes with acid).
- This may be shell fragments, mud, or small, round ooliths that form in tropical lagoons.
- Chalk is a soft white limestone made from the microscopic skeletons of marine plankton.
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