All metals are found in the earth, but not in a form that can be used straight away. They are generally combined with rock and other minerals to form an ore (such as the iron ore shown on the left). To release the metal, the ore is extracted from the ground. This is mostly done by mining, if the ores are buried deep in the rock. Sometimes, the ore is found closer to the surface. Gold, for example, can be found in river beds, where the action of the water has broken up rocks and released it.
Metals have been used by man to make objects for thousands of years, but to make the metal useable it has to be separated from the ore. The way in which this is done depends on the metal, but often involves grinding the ore and combining it with liquid to separate out the different parts, or heating it until the metal melts (this is known as smelting).
Some metals are more difficult to find or manufacture than others – the ores may be buried very deeply in the earth, or there is just not very much of it. This makes some metals more valuable and expensive than others.