A mineral is a naturally occurring, inorganic solid with an orderly internal arrangement of atoms (called crystalline structure) and a definite, but not fixed, chemical composition. Some minerals, such as gold and diamond, are single chemical elements. However, most minerals are compounds consisting of two or more elements. For example, the mineral halite is composed of the elements sodium and chlorine. The distinctive crystalline structure and chemical composition of a mineral give it a unique set of physical properties such as its luster, its hardness, and how it breaks. The fact that each mineral has its own characteristic physical and chemical properties can be used to distinguish one mineral from another.