Cement is made from clay and baked limestone that are crushed and mixed together, then heated in a special kind of oven called a kiln.

When water is mixed with cement it forms long thin crystals. They lock together and make a hard material.

Cement is mixed with sand and water to make a material called mortar. This is used to hold bricks or stones together. The crystals grow between the sand grains and into the surfaces of the bricks or stone to hold them together.