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Year 5 Science

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Making Rocks

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Mountains are made of rocks, but what are rocks made of? Rocks are made of chemicals called minerals. There are over 2,000 kinds of minerals on Earth. Some rocks are made of a single mineral, and others are combinations. To classify a given rock, geologists consider how it was formed. Rocks that were made from cooling magma or lava are called igneous [IG-nee us] rocks. The name comes from ignis , the Latin word for ‘fire’. Heavy, speckled granite; light, powdery pumice; black, glassy obsidian – even though they all look different, these are all igneous rocks. They started as hot magma and cooled into rock.

Rocks that were made when layer upon layer of sand and debris settled down together are called sedimentary rocks. Their name comes from the Latin word sedo , which means ‘settle down’. Over millions of years, layers of sediment pressed down in the bottom of ancient oceans and rivers. The pressure cemented tiny grains together into rock. Limestone is a sedimentary rock, made mostly of the compressed bones and shells of millions of tiny sea creatures. Sandstone is another sedimentary rock.

The last family of rocks is called metamorphic [met-uh-MORE-fick] rock. This family gets its name from the Greek word metamorphosis , which means a transformation or change of shape, because metamorphic rocks are rocks that have changed form. Some metamorphic rocks have changed through heat. When magma collects underground, it heats the surrounding rock to such high temperatures that the minerals become cooked. They change into new minerals, and the rocks containing them change form. Others have changed through pressure. Immense weight, like the weight of a mountain, can press down and change minerals. Marble, for example, used for its beauty in sculpture and buildings since the time of the ancient Greeks, is a metamorphic rock. Heat and pressure underground turn limestone into the rock we know as marble.

This activity is adapted from pages 319-320 of What Your Year 5 Child Needs to Know, which can be purchased here.