A mineral is a solid that has a crystal structure and a definite chemical composition. It is naturally occurring and generally inorganic. For example, a gem stone would not be a mineral because it is manufactured by people. Diamonds however are because they are mined from the earth by people. Natural emerald from the ground would be considered a mineral, but if it were to melt, it would not be considered a mineral. The smooth flat surface on a crystal represents a well-organize, internal structure of atoms.