Platinum, a silvery-white, metallic chemical element. Platinum and five other elements—osmium, iridium, paladium, rhodium, and ruthenium—make up the platinum group of metals. Platinum is a precious metal. In pure form, platinum is relatively soft. It is malleable (can be shaped by hammering) and ductile (can be drawn into a wire). For many purposes, platinum must be alloyed with other metals to harden it. Weighing 1,335 pounds per cubic foot (21,385 kg/m3), it is the third heaviest element, following only iridium and osmium.

Platinum does not tarnish and does not react with most chemicals. Single acids do not affect it, but it dissolves in aqua regia, a mixture of hydrochloric acid and nitric acid. Platinum is a good conductor of heat and electricity.

Platinum and platinum alloys have many uses. They are popular for fine jewelry. Platinum is used for laboratory apparatus such as crucibles and mixing tools. The spinnerets used in producing fiberglass and synthetic fibers are sometimes made of platinum. Platinum is also used for electrical contacts. Platinum is used as a catalyst (a substance that influences a chemical reaction without itself being changed) in automotive pollution-control devices and in the production of acids and gasoline.

The leading producers of platinum-group metals are South Africa, Russia, and Canada. Platinum occurs in a free form as small nuggets in gravel placers. It is also found combined in the ores of many metals and in the mineral sperrylite. Much of the North American production of platinum comes from the recovery of the metal during the electrolytic treatment of nickel ores. Another important source of platinum is platinum objects, which can be melted down so that the metal can be reused.

The existence of platinum was first officially recorded by Don Antonio de Ulloa in 1735 during an expedition in Peru. The name platinum comes from the Spanish for little silver.

Symbol: Pt. Atomic number: 78. Atomic weight: 195.08. Specific gravity: 21.4. Hardness: 4.3. Melting point: 3,222 F. (1,772 C.). Boiling point: about 6,900 F. (3,800 C.). Platinum has six stable isotopes—Pt-190, 192, 194, 195, 196, and 198. Platinum belongs to Group VIII of the Periodic Table and has a valence of +2 or +4.