Minerals are the building blocks of rocks. A mineral is an inorganic (nonliving) solid that has a regular internal arrangement of atoms and molecules. Each mineral has its own unique combination of different chemical elements. When atoms and molecules bond together to make a mineral, they usually form some type of crystal. Every species of mineral has its own special crystal structure. Over the years scientists have discovered about 2,500 different types of minerals, but most of these are rare. In fact most of the rocks that we find are usually made from fewer than 100 common minerals.