Discovered by Berzelius and Hisinger in 1803, but not isolated as a metal until 1875, cerium (named for the asteroid Ceres) is the most abundant of the so-called rare-earth metals. It begins the series of lanthanides that runs from elements 58 to 71. In pure form the element is a malleable and ductile metal, similar in coloring to iron. It is much more reactive than iron, however, readily oxidizing in moist air and releasing hydrogen from boiling water. Friction from abrading a sample can cause it to ignite.
Although the metal itself is too reactive for most uses, compounds of cerium are used in glass making and photography. It has limited use in some special alloys as well. Most commercial grade cerium is derived from monazite sand which is a mixture of phosphates of many of the rare earth metals along with calcium and thorium.
Stephen R. Marsden (ChemTopics)