As one of the rarer, less commonly seen metals, you could be excused for not knowing much about Iridium, but it has many uses. As a transition metal, it possesses a very high density and melting point of nearly 2,500 °C. Despite its rarity and relative anonymity, Iridium is one of the most important metals in science and nature, playing a very important role in multiple discoveries, processes and theories in the last two centuries.

The Story of Iridium Discovery

In 1803 Smithson Tennant, a chemist from Yorkshire, England, was investigating the known but little studied element Platinum. It had been noted prior that a black residue was left behind when dissolved in the acidic compound Aqua Regia. Until then, nobody had given much thought to the residue, being discarded as a valueless byproduct by French chemist Joseph Proust. But Tennant was curious and set about trying to identify the elements present in the residual matter. After using various methods to isolate and extract the mystery compound, including alternative applications of caustic alkali and acidic solutions, he isolated two separate metals from the material.

After more experimenting and refining, as one produced a distinctive odor throughout its refining process, he named one after the Greek word for smell; Osmium. The other displayed, due to its many diversely colored salts, an array of colors when illuminated.

For the second metal, he chose Iridium, from the Greek goddess Iris, the personification of the rainbow in Greek mythology.

What is Iridium used for and why is it in high demand?

Because it has a few unique properties, such as extremely high resistance to temperature and corrosion, and very low reactivity – even lower than gold – Iridium has a few unique but invaluable uses.

Spark Plugs and Electrical Contacts

Thanks to its low reactivity and high melting point, Iridium is perfect for electrical contacts in extreme environments, it is commonly used by NASA in electronic devices in working space. An application closer to home; the electrodes in spark plugs are exposed to temperatures of around 950°C and harsh chemicals, the material needs to be highly resistant in order to last a reasonable lifespan. Iridium coated spark plugs can last 25% longer and give a stronger spark than the competition. Recent increases in electric car production has seen the demand for iridium surge rapidly. With it too increasing the ore value and level of production across the globe. From March 2020 to March 2021 the raw cost of Iridium rose from $1,500 per ounce, to over $4,500.

The SI Metre Bar

Up until 1960, the unit Metre was ultimately defined by a physical object. This allowed a yardstick for all other standards and equipment to be based off.

To make measurements more accurate and repeatable, an alloy of Platinum and Iridium was created, this alloy selected due to its extremely high resistance to corrosion and reaction, as well as its very low thermal expansion coefficient. After 1960 however, the unit was defined theoretically, as the distance light travels in a set time, but the Metre bar still exists in a museum in Paris.

How is Iridium extracted?

Iridium is rarely mined exclusively, it is actually unearthed as a byproduct of mining Nickel and Platinum ore. For every 190 tons of platinum ore mined, only 7.5 tons of Iridium are found. After the ore is extracted, it is isolated from the platinum by various methods, including mixing in solution with sodium peroxide, and then extracting via aqua regia, the same basic process as used in 1803.

Why is Iridium so rare?

The simple answer is that there is very little iridium ore on the planet, as mentioned above, there is approximately 1/20th of the Iridium as there is Platinum, an already expensive material. Further to this, the process of refining Iridium is complex, with the low amounts globally not allowing the economies of scale of mass production to lower the unit cost much.

Iridium Facts

• It is the 9th rarest element on earth
• Iridium is the most corrosion resistant material known to man
• Meteors and Comets have a very high Iridium content
• The presence of large amounts of Iridium in the Earth’s crust gives evidence to the theory of Dinosaurs being made extinct by a comet about 65 million years ago
• It is the second densest material known to man, after Osmium
• Most Iridium mining takes place in South Africa, Alaska, Brazil and Russia