WHAT'S THE BIG IDEA?

Wherever you are now, there are rocks below you. Even if you are standing on the beach, digging in the garden, swimming in the sea or rowing across a river, there are rocks somewhere beneath your feet.

There are many different rocks, from soft mudstone and crumbly sandstone to hard granite. Some rock splits in sheets - like slate. Some rocks are rare and valuable - like gold and diamonds.

But why, if there are rocks everywhere, are they often covered in earth and stones? Rocks break down. Ice cracks them. Water tumbles them. They are rubbed together. They break into smaller and smaller bits. These small bits mix with the remains of plants and animals to make earth or soil.

Sandy soil has big bits in it. Water passes through it easily. The big bits are stopped by a sieve. Clay soil has tiny bits in it. It holds water. Its tiny bits pass easily through a sieve.

We can use rocks and soils in different ways. Hard rocks are good for building. Loam - a mixture of clay and sandy soil - is good for growing plants.

Most materials we use have been changed in some way. Clay is a natural material. To change clay permanently - to make a chemical change - we must heat the clay in a hot oven called a "kiln".