Science corner

8th October 2004 at 01:00
Sophie Duncan experiments with different rock types

Here are two experiments to investigate the properties of rock.

Geologists divide rocks into three main types - sedimentary, metamorphic and igneous. Sedimentary rocks are formed from compressed sediment - tiny bits of the Earth that have broken off over thousands or millions of years and collected in places such as riverbeds where they become pressed down together. They include sandstone and limestone. Igneous rock is formed when magma - the kind of molten rock that flows from volcanoes - solidifies.

Examples include granite and basalt. Metamorphic rock is formed from rock that has been subjected to heat and pressure - for example slate.

Rocks lying on the Earth's surface are damaged by the weather. Take samples of a variety of rocks. Encourage your students to handle them and to think about which rock would make a good mountain, or could be used in a building. Put the rocks in a plastic container, cover with water and place in a freezer. Once the water is frozen, remove the container of rocks and allow it to defrost. Observe any changes in the rocks and repeat the experiment several times, observing any changes.

Encourage your students to think about why some of the rocks have broken up more than others. Some rocks have gaps in them that let water in. When the water freezes it expands and the gaps get bigger. Eventually the rock is forced apart.

Take a selection of the different types of rock. Weigh each rock and place them all in a plastic container with a lid. Shake the container for 20 seconds and remove the rocks. Observe which rocks are most damaged and weigh them. Repeat the experiment several times. The sedimentary rocks will break down more readily than igneous and metamorphic rock.

Make a table of your results and encourage your students to discuss what would happen to cliffs made of the different types of rock and why.

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