(Click above to listen to this article read aloud.)

Rhodium is a rare metal used in jewelry, It’s also the most expensive metal in the world. It’s part of the platinum group of metals, alongside palladium, osmium, platinum, iridium, and ruthenium. 

Fast Facts

• Atomic Number: 45
  
• Melting Point: 3567 degrees Fahrenheit (1964 degrees Celsius)
  
• Boiling Point: 6683 degrees Fahrenheit (3695 degrees Celsius)
  
• Density:12.41g per cubic centimeter
  
• State at room temperature: Solid
  
• Atomic Symbol on Periodic Table: Rh

Appearance

Like most metals, rhodium is hard and silver. It’s very durable and long lasting, with high reflective qualities. Compared to platinum, it has a higher melting point and a lower density. It’s also in a group of metals called the ‘noble metals’ meaning it doesn’t react well with oxygen. Rhodium also has non-corrosive properties.

Where Can It Be Found?

We can find rhodium in the Earth’s crust, but as we mentioned before it’s pretty rare. The rarest of all metals. In fact, it’s only found as a byproduct of platinum. As such, mining it is a complex process. 

People mine rhodium in South Africa, or it’s also found in the river beds in the Ural Mountains of Russia. There are also small abundances of rhodium in Ontario, in Sudbury. South Africa accounts for 80% of rhodium mining globally. 

Discovery of Rhodium

Rhodium was first discovered by an English chemist called William Hyde Wollaston in 1803. He was extracting metals from platinum ore from South America, and through this process discovered a variety of new metals like rhodium and palladium. Both metals require platinum to grow, which means they are rare in nature and the pricing can be volatile since they’re so dependent on platinum. 

However, Wollaston first heard of the potential of a new metal from a French chemist Hippolyte-Victor Collet-Descotils. He saw platinum salts which were sometimes colored red and wondered if the difference in color was because of a different metal altogether. Wollaston managed to remove rhodium and palladium from the platinum and got a dark red powder. 

Rhodium comes from the greek ‘rhodon’ which means rose, and was named after its rose-like color. Wollaston dissolved the platinum ore in aqua regia and neutralized it in sodium hydroxide. Rubbing a series of experiments he used nitric acid to dissolve all the metals apart from palladium and rhodium. The palladium dissolved in aqua regia, leaving only the rhodium which he washed in ethanol. 

How is Rhodium Used?

Rhodium has a variety of uses in the modern day world. One of its most common applications comes as a catalytic converter in vehicles, turning harmful emissions into less toxic gases. 

However, it also gets used ornamentally in jewelry and decorations. It can be electroplated onto white gold or platinum to give the jewelry a white reflective surface, and can also coat silver to stop it from tarnishing over time. Solid rhodium jewelry would be incredibly expensive, and is also very rare because it has such a high melting people and isn’t malleable. 

We have also used it as an alloying agent because of its resistance to oxidation and corrosion, which have several applications in electrical contacts. 

The Most Valuable Metal

So there you have it! All the information you need on the rarest metal on our planet. While you won’t be getting rhodium jewelry anytime soon, now you’ll at least be able to pass a quiz on it!