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Rocks

 

There are three categories of rock- igneous, sedimentary and metamorphic.

 

igneous rocks

Igneous rocks originate deep in the Earth. They erupt from volcanoes as magma and cool or solidify as they rise to the upper layers. Basalt is an igneous rock and so is granite, a very hard rock often used in building . Pumice stone is a soft igneous rock that is ejected from volcanoes. As it cools, it often fills with so many air bubbles that it floats in water.

 

sedimentary

Sedimentary rocks can be formed by deposits in water and occasionally by wind. Sandstone is a common example. Organic sedimentary rocks are formed by living plants and animals – coal comes from plant matter and limestone from the  calcium from billions of plants and animals. chemical sedimentary rocks occur when chemical processes take place and minerals are deposited.

metamorphic

Metamorphic rocks are Igneous or sedimentary rocks that have changed as a result of high temperatures or pressures. State used on roofs is a familiar example.

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