NATURAL SCIENCE. UNIT 3: ROCKS AND LANDSCAPES

● Rocks and minerals

▪ What are rocks?

The Earth’s crust is formed from materials called rocks.

They form the land in whick we live, the mountains, the bottom of the sea, etc.

Rocks are the solid substances which form The Earth’s crust. They are made of other solid substances called minerals.

The little grains we see in a rock are the different minerals which form it.

Some rocks are made of a lot of similar grains: these rocks are formed from one mineral.

Other rocks are made of many different grains of different colours and sizes: these rocks are formed from different minerals.

▪ Characteristics of rocks

Rocks are characterized by different things:

* Composition: the combination of minerals a rock is made of. It affects its hardness, colour, etc.

* Texture: the form and arrangement of the minerals a rock is made of.

* The form in which they appear in nature. Some rocks are found in layers, others in enormous blocks, and some in volcanoes.

▪ Some types of rocks

♠ Limestone: it is a soft rock which can be white, grey or cream. It is formed from a mineral called calcite. It sometimes contains fossils which are the remains of living things from long ago.

♠ Slate: it is a hard rock which is usually dark grey or black. The minerals it is made of are arranged in thin layers. It breaks easily into thin sheets.

♠ Granite: it is a very hard rock which is usually grey. It is formed from three different minerals (cuarzo, feldespato y mica).

♠ Basalt: it is a very hard rock which is dark grey or black. It is made of different minerals. It is formed in volcanoes.

● Rocks and human beings

▪ How we use rocks

Human beings use the different types of rocks for different purposes. In some cases, we use them in their original form for construction, for decoration, to make things, etc. In other cases, we use only one of their minerals as base to make other materials like iron, glass or cement.

* Rocks for construction and decoration

- Granite, basalt and limestone are all used to build buildings. Slate is sometimes used to make roofs.

- Marble is a beautiful form of limestone and it is used to make floors and statues.

- Clay is use to make roof, bricks and containers. We model it and then heat it.

* Rocks from which we obtain minerals

- Iron, copper and aluminium are obtained by transforming the minerals there are in some rocks.

- Glass is made by melting quartz. Quartz is in granite and in some types of sand.

- Cement is made by mixing calcite, a mineral which comes from limestone, with other minerals.

▪ The extraction of rocks

Rocks are sometimes on the surface of The Earth and sometime very deep inside The Earth’s crust. To extract them we have to excavate them in mines. There are two kinds or types of mines:

♠ An open cast mine is used to excavate rocks near The Earth’s surface. It is a huge hole in the ground.

♠ An underground mine is a series of tunnels underground, inside The Earth’s crust. It is used to reach rocks deep underground.

▪ How do rocks influence our lives?

Rocks influence the lives of human being in a lot of ways.

* In a region with mines there is a lot of work and money for the people who live there. But it also damages the countryside and the environment and can damage people’s health.

* When a volcano erupts, very hot melted rocks come out of its crater. This can be very dangerous for people who live near.

* An earthquake moves the rocks of The Earth’s crust. This can damage towns and cities and cause a lot of problems for people who live there.