A metallic chemical element, symbol Al, atomic number 13, atomic weight 26.98154, in group 13 of the periodic system. Pure aluminium is soft and lacks strength, but it can be alloyed with other elements to increase strength and impart a number of useful properties. Alloys of aluminium are light, strong, and readily formable by many metalworking processes; they can be easily joined, cast, or machined, and accept a wide variety of finishes. Because of its many desirable physical, chemical, and metallurgical properties, aluminium has become the most widely used nonferrous metal.