10g sample of cerium in an ampule under argon. Image copyright: smart-elements.com.

Cerium (Ce) is a soft, ductile, iron-gray metallic element, the most abundant of the lanthanides (and more abundant than tin or lead). It was first isolated by J. J. Berzelius and W. Hisinger in Vestmanland, Sweden, in 1803, and is named after the asteroid Ceres, discovered in 1801. The chief ore is monazite. Cerium is used in making pocket lighter flints), in alloys catalysts, nuclear fuels, and special glass and ceramics, and as the core of carbon electrodes in arc lamps. However, its use is restricted by the fact that it tarnishes easily, reacts with water, and burns when heated. Its most common isotope is 140Ce (88.48%).

atomic number 58
relative atomic mass 140.12
relative density 6.77
melting point 798°C (1,468°F)
boiling point 3,257°C (5,895°F)