Lutetium gets its name from Lutetia, the ancient Roman name for Paris, the city where it was discovered. However, that Latin name originally referred to a small settlement on the Seine rather than the grand city Paris would later become.

It was discovered independently in 1907 by three chemists: Georges Urbain in France, Carl Auer von Welsbach in Austria, and Charles James in the United States. However, Urbain received credit for the discovery because he published his results first, earning him the right to name the element.

Welsbach had actually wanted to call it cassiopeium, after the constellation Cassiopeia, but lost the naming battle to Urbain’s choice of lutetium.

Despite being identified in 1907, a pure sample of the metal wasn’t isolated until 1953.

Lutetium sits at the very end of the lanthanide series and is generally considered the heaviest rare earth element, as well as the hardest and densest.

It’s also the least abundant naturally occurring rare earth element, which makes it expensive. This scarcity is partly explained by the Oddo-Harkins rule, since elements with odd atomic numbers, like lutetium’s 71, tend to be less abundant than their even-numbered neighbors, such as ytterbium.

Even so, it’s actually more common in the Earth’s crust than silver or gold.

Its price has fluctuated dramatically over time. It was once the most expensive element on Earth, costing roughly six times as much as gold, though today it costs closer to a quarter of gold’s price.

The element is extracted, with considerable difficulty, from minerals such as monazite. Its small atomic size allows it to fit into the crystal lattices of other minerals, meaning trace amounts can be found in nearly every yttrium-containing mineral.

Lutetium is a silvery-white metal that is relatively stable in air but reacts with water and dissolves in acids. Its compounds are colorless because its filled 4f electron shell makes it spectroscopically “transparent.” This contributed to the difficulty of identifying it, along with its status as the last stable lanthanide to be discovered.

Lutetium’s practical uses are limited but notable.

It serves as a catalyst for cracking hydrocarbons into gasoline in oil refineries, while a radioactive isotope, lutetium-177, is used in targeted cancer therapies.

Lutetium tantalate is one of the densest known white materials, making it valuable for X-ray detectors because it emits light when struck by X-rays.

Different isotopes of the element span an enormous range of stability. Lutetium-176 is radioactive, with a half-life of about 37 billion years, making it useful for dating meteorites and geological events. Meanwhile, lutetium-150 has a half-life of just 45 milliseconds, making it one of the shortest-lived lutetium isotopes.

The element also has a cosmic side. It can be detected in the Sun through absorption lines in the solar spectrum, and lutetium-176 is primarily formed in red giant stars through the slow neutron capture process known as the s-process.

Lutetium has no known biological role in the human body and is considered to have low toxicity.

The discovery of lutetium also created some lasting confusion in chemistry.

Urbain mistakenly believed he had discovered element 72 and named it “celtium,” but it later turned out to be nothing more than purified lutetium. French chemistry textbooks continued to insist that celtium existed for years until X-ray spectroscopy finally disproved the claim.

Even today, there’s some debate over whether lutetium or lanthanum should technically begin the f-block, since lutetium’s filled 4f shell leads some periodic tables to place it under scandium and yttrium in Group 3 instead.