Lanthanum carries atomic number 57, placing it at the very beginning of the lanthanide series on the periodic table.

Its chemical symbol, La, is a straightforward two-letter designation that has remained consistent since the element first received its name.

The label “rare-earth element” is something of a misnomer where lanthanum is concerned. It actually occurs in Earth’s crust in greater quantities than lead.

Swedish chemist Carl Gustaf Mosander identified lanthanum in 1839 by successfully separating it from cerium compounds that had previously been assumed to contain only cerium.

The name chosen for the element reflects exactly how it was found. It derives from the Greek word lanthanein, meaning “to lie hidden,” a reference to the fact that it had been concealed within minerals no one suspected held anything new.

In its pure state, lanthanum is a silvery-white metal, though exposure to air causes it to tarnish relatively quickly.

The metal is soft enough that a standard knife can cut through it without difficulty.

Among rare-earth metals, lanthanum ranks as one of the more chemically reactive members of the group.

When air reaches the surface of lanthanum, it reacts with oxygen to form lanthanum oxide, leaving a white powdery layer across the metal.

Contact with cold water produces a slower reaction, but lanthanum does respond, releasing hydrogen gas in the process.

The element has an atomic weight of approximately 138.9055. It melts at around 918 degrees Celsius, a temperature high enough to liquefy aluminum with considerable margin to spare. Its boiling point climbs to roughly 3,464 degrees Celsius.

Lanthanum compounds play a role in petroleum refining, where they assist in breaking down crude oil into usable fuel products.

Nickel-metal hydride batteries, which power many hybrid vehicles, frequently incorporate lanthanum-containing alloys as a functional component.