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Sedimentary Rocks

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 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 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 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 and 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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