Iron

What is iron? Iron is the most common element of the Earth, although most of it is deep below the Crust. Iron is a grey-coloured metal. Iron mixed with carbon is called steel. Steel is used for a wide variety of purposes such as car bodies.

The world's oldest iron bridge, ironbridge, Shropshire, England.

Iron is a chemical element. Scientists give it the symbol Fe because the Latin for iron is ferrum. It is the most common element on Earth, because it makes up much of Earth's outer and inner core. But we cannot reach it close to the Earth's centre. The part of the Earth we mine it from is called the crust. Here it is the fourth most common element. Why is it so common? Because it is one of the elements that finally form after the explosion of a giant star. As a result, of such explosions, it gets scattered into space as dust and the dust finally gathers into planets.

Iron is rarely found on its own on Earth. It is found in pure form in meteoroids, because they are parts of that space dust mentioned above. But iron easily combines with oxygen and water on Earth. So whereas if we were to see pure iron we would see a grey metal, normally we see it as a rock combined with oxygen and water, and in that form it is red. If ever you see a reddish or brownish rock, that colour is due to iron. You can see this difference if you look at how a piece of iron (made in a blast furnace) changes in damp air. A nail, for example, rusts. The nail is fresh iron; the rust is iron combined with oxygen and water.

Iron is different from many metals in combining with oxygen. A piece of aluminium, for example, combines with oxygen to form a very thin coat which takes the shine off the aluminium, but otherwise protects it from the air. Iron, on the other hand, combines with oxygen in such a way that makes it swell up. This means that it blisters off the iron, and flakes fall away, leaving more iron to rust. That is why we have to paint iron, but not aluminium.

Iron metal has been used since ancient times, and gave rise to the term Iron Age. Iron only melts when it is much hotter than some other metals, such as copper (which can be combined with tin to make bronze), and that is why the Iron Age began after the Bronze Age. It took time for people to work out how to make a fire hot enough (they eventually used bellows).

Interestingly, and this may surprise you, because you are used to iron being used for its hardness, pure iron is softer than aluminium. But it is very difficult to obtain pure iron. When it is heated in a large blast furnace, it is not pure, but contains some other elements such as carbon.

It took many hundreds of years for people to discover that the amount of carbon could be varied. When they knew how to control this, they were able to make steel, which is up to 1000 times harder than pure iron. For this it needs 1-2% carbon. Carbon comes from the coke that is used to melt the iron in a blast furnace.

Heating and melting iron ore is called smelting. The iron ore is put in a tall furnace with coke (partially burned coal) and some limestone (to help the process) and oxygen is blown in from below. The iron ore gets very hot, and the iron splits into molten iron, which being heavy flows to the bottom of the furnace, and the rest of the rock, which being much lighter floats to the surface and is called slag. The liquid iron is allowed to flow out of the furnace and it is collected in large moulds. The iron can then be made into different shapes, or processed further into steel.

Steel is the most common metal used in industry. Steel is used to make cars and bridges for example. It makes the steel rods in reinforced concrete and the frames for many school and office chairs and tables. It makes the cases for cookers, fridges, washing machines and so on and so on.

Iron is an important part of all living things. For example, it is part of our red blood cells. Because iron combines with oxygen, the red blood cells are able to pull oxygen out of the air and carry it around the body. Plants also use iron.

Iron can combine with some other elements to give very beautiful materials. The video below shows yellow cube-shaped crystals of 'fool's gold', which is a combination of iron and sulphur.

Video: Iron ore (red haematite)
Video: Iron pyrites
Video: Magnetitie (magnetic iron)

Explore these further resources...

(These links take you to other parts of our web site, never to outside locations.)

You can search in these books:


You can look in this topic for more books, videos and teacher resources:

Jump to Dinos, rocks, minerals, fossils, evolution toolkit screen
The toolkit screen link will take you to a library containing a selection of:
an i-topic, more books, pictures, videos and teacher's stuff related to the search word.
© Curriculum Visions 2018