Rhodium: The Rarest and Most Valuable Precious Metal on Earth

On Christmas Eve in 1800, English scientist William Hyde Wollaston acquired a piece of nearly pure platinum ore, which he secretly bought and smuggled from the Spanish colony of Nueva Granada (modern-day Colombia) for £795 ($1,051.99 in 1800 — equivalent to $23,206.23 today).

He was optimistic, believing he could develop a new chemical process to make the solid ore malleable like platinum. However, the sample contained a secret of its own — a new, rare metal that had never before been discovered in science.

Today, rhodium is the most prized precious metal on Earth: a chemical element symbolized by Rh and carrying the atomic number 45.

Rhodium Metal: An Unexpected Discovery

In just a few years, armed with his smuggled platinum ore, Wollaston achieved what earlier scientists could not: he developed a chemical method that isolated platinum and made it malleable.

While dissolving the platinum ore in his backyard garden lab, Wollaston ended up with both soluble and non-soluble residues. Upon precipitating the soluble solution, he observed that reddish salts remained.

Red salts were unusual for platinum, and Wollaston suspected something else was present in the sample. In 1803 and 1804, he revealed that, along with platinum, he had discovered two new precious metals: one he named palladium, and the other, rhodium.

What Is Rhodium?

Rhodium is a highly reflective, corrosion-resistant metal that has found applications in various industries, such as automobiles, jewelry, chemicals, and electronics. As explained by Shaun Peterson, Gemological Institute of America (GIA) supervisor of jewelry manufacturing arts research and development, the scarcity of rhodium and its wide range of uses contribute to its high value.

"The rarity of rhodium and the significant global demand, particularly due to its use in automotive manufacturing, have led to a substantial rise in its price," says Peterson. New emissions regulations, especially in China and Europe, are likely responsible for the surge in rhodium prices.

As of today, the cost of rhodium stands at $14,000 per ounce. In comparison, platinum is priced at $959/ounce, palladium at $1,866/ounce, and gold at $1,783/ounce.

Rhodium is never found in its pure form. Instead, it is typically extracted as a tiny byproduct of refining platinum, copper, and nickel.

If you're looking to find rhodium, your best bet is to board a flight to South Africa, the leading producer thanks to its expansive platinum mining industry. Rhodium can also be found in the river sands of North and South America, or in the copper-nickel sulfide ores of Ontario, Canada.

A Rose (Metal) by Any Other Name

Wollaston named one of the newly discovered metals rhodium, derived from the Greek word for rose, "rhodon", because of the reddish salts that dissolved in the aqua regia. (Aqua regia is a yellow-orange, fuming liquid, so-named by alchemists for its ability to dissolve noble metals like gold and platinum.)

"Rhodium belongs to the platinum metals group, which is classified as one of the noble metals," explains Peterson.

Other Platinum Group Metals

The platinum group metals (PGMs) consist of six elements:

These metals share similar properties and are often found together in nature. Much like gold and silver, they are classified as precious metals. "Key qualities that define precious metals include their appeal, malleability, durability, and scarcity," Peterson points out.

Rhodium is Typically Not Dangerous (Unless You're a Jeweler)

Rhodium has been extracted as a by-product of platinum since the 1930s when substantial platinum ore deposits were discovered in the Transvaal region of South Africa. Since then, there has been no definitive evidence of harm to humans, primarily because it is highly unlikely for people to encounter significant amounts of rhodium.

Studies on plants show that rhodium is the least toxic of the platinum group metals, but due to its naturally scarce occurrence, no tests have been conducted on humans.

When inhaled, rhodium can pose serious risks, especially in jewelry making. Peterson points out, "During the rhodium plating process, fumes are released that can be hazardous. Because of these health risks, safety precautions are implemented during the plating process to prevent inhalation."

Rhodium: Enhancing Our Environment and Jewelry's Shine

What do cars, jewelry, and gum all share in common? Surprisingly, they all involve a bit of rhodium.

A significant portion of available rhodium — 80 percent — is used in catalytic converters within vehicles to help reduce harmful exhaust emissions. Rhodium is particularly effective in breaking down nitrous oxide (NOx) molecules, the toxic, brownish gas produced by fossil-fuel-powered vehicles, including cars, trucks, boats, power plants, and turbines, among other sources.

While NOx emissions can cause severe damage to our bodies and the ozone layer, the situation would be much worse without rhodium's crucial role in mitigating these effects.

Rhodium plays a crucial role as a catalyst in the production of nitric acid, acetic acid, and hydrogen reactions, as well as in the creation of menthol — the minty flavor found in chewing gum. Its corrosion resistance and excellent electrical conductivity also make it ideal for coating optic fibers and optical mirrors, headlight reflectors, and various electrical components.

Rhodium is most commonly encountered in its gleaming, lustrous form in jewelry. According to Peterson, "Jewelers favor rhodium in the creation of jewelry due to its bright, silvery-white color, extreme hardness, and ability to enhance scratch- and corrosion-resistance." He adds, "It is also hypoallergenic, making it a safe choice for those who may have allergies to certain metal alloys used in jewelry."

Rhodium is free of nickel, so even those with the most sensitive skin can confidently wear a rhodium-plated bracelet without concern.

Rhodium: A Tough Metal to Work With

With a melting point of 3,565 degrees Fahrenheit (1,963 degrees Celsius), rhodium is incredibly hard and difficult to manipulate. Its high melting point makes it more challenging for jewelers to work with compared to other metals.

"Rhodium alone is too hard for typical jewelry making," Peterson explains. "The most common application of rhodium is as a plating over other metal alloys, either to offer protection from allergies or to enhance the appearance of the jewelry."

While rhodium's luster, shine, and durability are definite advantages, its extreme hardness makes it difficult to work with, resulting in a thin plating that can wear off relatively quickly.

"The downside," Peterson notes, "is that rhodium plating is only a thin layer that coats the jewelry. As a result, over time, the rhodium layer will diminish due to regular wear and tear." Jewelry makers prefer to apply rhodium to pieces that experience less friction, like earrings or necklaces, and typically recommend replating every one to two years.

Because only a small amount of rhodium is needed to plate a piece of jewelry, it is generally affordable. Rhodium-plated jewelry can be found online priced between $300 and $5,000, but the price difference is primarily due to the designer, base metal, and inclusion of gemstones, rather than the rhodium itself.

Thanks to Wollaston's discovery of rhodium more than two centuries ago, we can now enjoy wearing and driving with this valuable and rare metal.