Sb, or antimony, is a chemical element with the symbol Sb and atomic number 51. It is a metalloid, meaning it has properties of both metals and nonmetals. Antimony is primarily used in alloys to improve their hardness and mechanical properties, as well as in flame retardants and batteries. This element is found in nature mainly in the form of stibnite, a sulfide mineral. Antimony has been known since ancient times and was used in cosmetics and medicine. Today, it is also important in the production of semiconductors and various electronic devices.