Cement is formed by heating limestone and clay. Powdered clay and limestone are roasted in a kiln to produce a complex mixture of calcium and aluminium silicates. This is cement.

When cement is mixed with water, a slow chemical reaction takes place that causes the cement to slowly set hard. It is used to bond bricks together in building. It is also often mixed with sand and chippings to make concrete, which is a very quick and cheap building material. Many consider it unattractive, however.