The best known precious metals are gold, silver, and platinum. (Platinum is also known as white gold)
Precious metals are precious because they are rare.
Gold and silver are used to make coins.
Gold, silver and platinum are used to make jewellery.
A metal is said to be precious if it is rare. Gold, silver, platinum and other precious metals are found inside rocks that are dug out of the earth at mines.
Gold is a yellow and shiny. Gold is the heaviest metal, but is not very hard. Because it's soft gold is easy to make into many shapes. It can be made into fine threads like wire or it can be hammered into thin sheets.
To make gold hard it is mixed with other metals such as silver and copper. When this is done the mixture is called an alloy. Gold alloys can then be used to make coins and all kinds of jewellery.
Gold is mined in two ways. Open-cut mining and underground mining.
Open-cut mining is used to get gold, silver and platinum out of the Earth. Open-cut mining is used when the rocks containing gold are near the surface. The soil and the top layer of rock is scraped away using large machines. The the earth is broken up using explosives and the broken rock is taken to a mill where it is crushed.
Underground mining is done deep under the ground in tunnels. Holes are drilled into the rock face at the end of a tunnel and explosives are placed into the holes. The explosions blast the rock into pieces. The broken rock is taken out of the mine to a mill where it is crushed and the- gold collected. Tunnels are dug deep underground to get gold and silver
Separating gold from the rock
One way to separate the gold from the crushed rock is to roast it or mix it with bacteria. Another way is to dissolve the crushed rock in a chemical called cyanide (say: sie-an-ide) The separated gold is washed, filtered and then melted in a furnace. The molten gold is poured into a bar shaped mould and cooled.
Gold mining and the environment
Gold mining can be harmful to the environment because:
- Air is polluted by dust from open-cut mines.
- A dangerous gas can escape into the air when the crushed rock is roasted. This gas, sulphur dioxide, causes acid rain.
- The land is affected by the removal of soil and plants when mining takes place.
- Dirt washes into rivers and streams from mine sites.
- Poisonous cyanide, used in gold mining, pollutes waterways too. It kills plants and animals in the water and animals and people who drink it.
Although miners might try to reduce the effects of mining on the environment, accidents happen and some miners don't take enough care to reduce the damaging effects of mining on people and the environment.
Silver is a soft, white metal. It is harder than gold and is used to make coins, jewellery, tableware and in photography. Gold and silver are used to make coins and medals Silver is mined in similar ways to gold.
Silver is found in rock that also contains copper and lead. The silver is separated from the crushed rock when the rock is roasted. The silver is cleaned, filtered, then melted and poured into bar shaped moulds.
Platinum is a silver - white metal. It is very rare. Platinum is used to make jewellery, including watches. Platinum is dug from the earth in mines.