Platinum

Last updated: May 30, 2010.

A column of platinum the size of a man is about 250 times heavier (it weighs an amazing 3540 kg or 47,000lb)! Platinum is a dense, expensive, and relatively rare, silvery-white metal—and those may be the only things you know about it. The name "platinum", which comes from the Spanish word platina (meaning "little silver"), relates to when and where the metal was discovered (in Latin America in the early 18th century). Platinum is a relatively recent human discovery compared to such age-old metals as iron and copper, but it's rapidly found important uses. You probably know that it's the magic ingredient in pollution-busting catalytic converters that help to keep our streets free of traffic fumes, but it's also used in dental fillings, scientific equipment, and jewelry.

Photo: Rich pickings: The Kondyor Massif in Eastern Siberia, Russia is a natural ridge about 10km (6 miles) across packed full of minerals, including platinum. Photo by courtesy of NASA Jet Propulsion Laboratory (NASA-JPL).

What is platinum?

It's not something you stumble across every day. Platinum is only the 72nd most common chemical element in Earth's crust—and, given that there are only 94 natural elements anyway, that makes it pretty rare. That's largely why platinum is so expensive. Currently it costs around $50,000 or £25,000 per kilogram (which is about $22,000 or £11,000 per pound). So the adult-sized block we spoke about earlier would set you back a cool $80 million or so.

You can find platinum (atomic number 78) buried deep in the middle of the periodic table in group VII among elements collectively known as the transition metals. Its near neighbors include iridum, osmium, palladium, rhodium, and ruthenium—five metals which, with platinum, are often called the platinum metals. They're well known for their catalytic properties: they help to speed up chemical reactions without themselves changing in the process. Platinum's catalytic properties have been known since the 1820s, when they were first discovered by German chemist Johann Wolfgang Döbereiner (1780–1849).

Although platinum earned its name only in the 18th century, the platinum metals (and alloys rich in platinum) were known in ancient times. Platinum is thought to have been described for the first time in 1557 by Italian chemist Julius Scaliger (1484–1558), though it was found in large quantities only in 1750 when Spaniards minining for silver in Rio Pinto, Colombia discovered it as an impurity and named it "little silver" (it's also sometimes called "white gold").

Unlike many elements, platinum can be found in its pure metallic form in nuggets, alloyed with other platinum metals, or as part of a mineral ore called sperrylite (platinum arsenide). It's located and mined all over the world, although the biggest producers (in order) are South Africa, Russia, Canada, Zimbabwe, United States, and Colombia (see the chart in the box). The only dedicated platinum mines in the United States are in south-central Montana, though some platinum is also made as a byproduct of copper refining in mines in Texas and Utah.

What is platinum like?

Physically, platinum is heavy, soft, malleable (easy to work—only silver and gold are easier to shape), and ductile (easy to draw into wires) and has a fairly high melting point (~1770°C or 3220°F). Chemically, it's often described as a noble metal because it is so unreactive. It doesn't even react with oxygen in air so it doesn't rust or tarnish. It's also reasonably resistant to attack from acids.

What's it used for?

Photo: This low-temperature oxidation catalyst, made from tin oxide and platinum, can turn toxic carbon monoxide into harmless carbon dioxide. In future, devices like this could protect homeowners from fumes produced by poorly maintained heating appliances. Photo by courtesy of NASA Langley Research Center (NASA-LaRC).

If you know platinum at all, you probably know it as the "magic metal" that helps catalytic converters to strip out pollutants from car engine exhaust gases, but it's so expensive that other platinum group metals such as palladium are often used in its place. The ease with which platinum can be shaped and its inertness (chemical unreactivity) makes it particularly suitable for jewelry. Unreactivity also makes it  useful in dental fillings, surgical tools, and apparatus for scientific laboratories. Apart from that, platinum finds important uses in the electrical industry, in lasers, and in making photographic materials.