Aggregates are a combination of crushed rock (of which there are three main types: igneous, metamorphic and sedimentary) and sand and gravel. Crushed rock, sand and gravel are also used to make value-added products such as lime, asphalt, concrete and mortar. Aggregates can only be extracted where nature has placed them. A line drawn roughly from The Wash to Portland Bill would separate the two basic types of aggregates found in the UK.

Over recent years, the sea-bed around our shores has become an increasingly important contributor to national supply needs. The marine aggregate industry satisfies much of the UK’s sand and gravel needs.

Synthetic aggregate also offers an excellent environmentally-friendly alternative to quarried aggregate. This is produced from pulverised fuel ash (PFA) - a by-product of coal-burning power stations.

• How hard rock is quarried
• How sand and gravel is quarried
• How marine aggregate is extracted