The metallic element, Bi, of atomic number 83 and atomic weight 208.980 belonging in the periodic table to group 15. Bismuth is the most metallic element in this group in both physical and chemical properties. The only stable isotope is that of mass 209. It is estimated that the Earth's crust contains about 0.00002% bismuth. It occurs in nature as the free metal and in ores. The principal ore deposits are in South America. However, the primary source of bismuth in the United States is as a by-product in refining of copper and lead ores.