The ground we walk on, build on, and grow gardens on, is made of rock. All the rocks in the world are made up of chemicals called minerals. Through a microscope a rock shows that it is made of crystals of different minerals all growing together like a mosaic.

Each mineral has its own chemical composition, and there are usually no more than half a dozen types in each rock. Three types of rock make up the Earth’s crust. Rocks are formed in three different ways to produce igneous, metamorphic and sedimentary rocks.

Igneous rocks form when molten magma cools and solidifies. Metamorphic rocks form when heat or pressure to form a new rock type chemically changes a rock. Sedimentary rock forms when fragments of rocks and other debris are cemented together.

Lead is a metal, and its metal point is 328 degrees. Its main natural source is the sulphide. Its good corrosion resistance and easy workability led to its early use in plumbing, and for containers for corrosive liquids. These uses had considerable toxic effects, as lead is slowly oxidised in the presence of air and water. Lead is used in quantity for the production of accumulators, that is storage batteries.

Lead has a high density. For this reason it is a good barrier to radiation. This is put to use in the nuclear industry and hospital x-ray departments, where the staff wear lead aprons. These aprons are made by baking a mixture of fine lead power and plastic to make a flexible sheet. This is then cut out to the right shape.

Lead shot can cause pollution in the wild. Birds that swallow it are gradually poisoned.

The sparkle of crystal is the result of adding lead oxide to glass. The lead also makes crystal softer. This means that designs that will glitter can be cut into it.