The average abundance of bismuth in the Earth's crust is about 0.00002%. It is most commonly found as an oxide, sulfide, or carbonate in silver, lead, zinc, and tin mineral deposits. The metal is a by-product of the smelting of these ores. Bismuth metal has a melting point of 271 deg C (520 deg F) and a boiling point of 1,560 deg C (2,840 deg F). On freezing, molten bismuth expands 3.3% by volume, a property shared by only one other element, gallium. Bismuth forms compounds in the +3 and +5 oxidation states; the +3 state is the more stable of the two. The metal dissolves in nitric acid to form bismuth nitrate, which on controlled hydrolysis produces bismuth subnitrate. Other mixed oxide salts of bismuth are similarly named.
The very low toxicity of ordinary bismuth salts permits their use in the cosmetic and pharmaceutical industries. An important new application is the use of the complex salt bismuth phosphomolybdate as an industrial catalyst in the synthesis of acrylonitrile, an intermediate product in the manufacture of acrylic fibers and various plastic products.