The most useful of all rocks

Limestone is, without doubt the world's most useful rock and we are fortunate that there is plenty of it around the UK.

We use limestone in three main ways:

1 Cut to shape

• as a building and ornamental stone

2 Crushed

• to make concrete
• for the different layers in our roads

3 Finely ground

• to make cement and iron
• to remove the sulphur from power station gases
• to add calcium to animal feeds
• to neutralise acids in wine and beer making
• to make lime for a variety of industrial and agricultural processes

How do quarries work?

There are around 1,300 quarries in the UK meeting our needs for aggregates.

They are of two main types:

Rock quarries

Rock quarries are usually much deeper and are dug on several different levels or "benches". The first stage is usually a carefully controlled explosion that releases and breaks up the rock into large lumps. A large truck or conveyor then takes it to a powerful crusher where it is broken down into fragments and separated into different sizes.

Sand and gravel quarries

Sand and gravel quarries are rather shallower because the deposits are usually only five or six metres thick. The material is dug with a mechanical shovel or a dragline and is then carried by conveyor to a plant where it is washed and separated into different sizes.

In both cases ,the aggregates are then delivered to customers by lorry (90%), by rail (5%) and by sea (5%). Rail transport is used where the aggregates need to be carried over longer distances such as from the Mendips or the Midlands into London.

Amazing rocks

Rocks are also used in lots of less obvious ways.

For example:

• Ground chalk is added to bread to give us calcium
• Salt is added to our food during cooking
• Pills consist of a small quantity of drug absorbed onto a "carrier" such as white clay
• The abrasive in your toothpaste comes from limestone
• Clay is used in face creams

Rocks as aggregates

Aggregate is the term we use for rock that has been broken into small pieces, either by nature or by people. We use around 200 million tonnes of aggregates every year, most of it for building.

Aggregates are of two main types of crushed rock, sand and gravel. If you draw a line across the UK between Humberside and Dorset you will find plentiful sand and gravel deposits to the south of that line and hard rocks to the north. Sand and gravel is rock which nature has already broken into fragments, mostly by weathering and by erosion during the ice age.

But not all aggregates are taken from the land. About 21 per cent of the sand and gravel needs of England and Wales are supplied from the sea. Most of this comes from licensed areas in the North Sea and off the South Coast. Smaller licensed areas exist in the Bristol Channel and in Liverpool Bay.

For more information about rocks as aggregate click here

Restoring the land

Quarrying is a temporary rather than permanent use of the land. Sand and gravel quarries may last no longer than 15 years and the land that has been dug is restored in stages. This may involve returning the land to farming with no obvious sign that it has ever been quarried. But it might instead provide an opportunity to create a nature reserve or sports pitches.

Because they are much deeper, rock quarries take much longer to restore but they too may be given back to farming or used to create nature areas. There are lots of examples of sites that have been quarried and are now more exciting and interesting as a result.

For more information about restoring the land click here.