Cerium is a chemical element with the symbol Ce and atomic number 58. It is the second element in the lanthanide series, and is classified as a rare-earth metal. Cerium is a relatively abundant element in the Earth's crust, and is found in a number of minerals, including monazite, bastnäsite, and allanite.

Cerium is a soft, ductile metal with a silvery-white color. It is the most reactive of the lanthanides, and tarnishes quickly in air. Cerium is also pyrophoric, meaning that it can ignite spontaneously in air when finely divided.

Cerium has a number of applications, including:

* As an alloying agent in steel, where it improves the strength and toughness of the metal.

* In the production of Mischmetal, a mixture of rare-earth metals used in a variety of applications, including lighter flints and electrodes.

* As a catalyst in a number of chemical reactions, including the refining of petroleum and the production of plastics.

* In the manufacture of phosphors, which are used in lighting and in cathode ray tubes.

* In the production of polishing powders and abrasives.

* In the production of permanent magnets.

Cerium is a relatively non-toxic metal, and is not known to cause any significant health problems. However, it is important to note that cerium can be an inhalation hazard, and can cause skin and eye irritation.