Be -Bi- is a chemical element with atomic number 83. Bismuth, a trivalent metal, resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead, and brittle, with a silvery white color, and often a pink tinge owing to the surface oxide. Bismuth metal has been known from ancient times, although until the 18th century it was often confused with lead and tin, which each have some of the metal's physical properties. Bismuth is the most naturally diamagnetic of all metals, and only mercury has a lower thermal conductivity.