Cerium
. Cerium, symbol Ce, soft, gray metallic element that is the most abundant of the rare earth elements . Cerium is in the lanthanide series of the periodic table (see Periodic Law ); its atomic number is 58. Cerium was discovered in 1803 by the Swedish chemists Baron Jöns Jakob Berzelius and Wilhelm Hisinger, and in the same year, independently, by the German chemist Martin Heinrich Klaproth ; the pure metallic element was not isolated until 1875. Cerium ranks 26th in natural abundance among the elements in the earth's crust. It occurs with other rare earth metals in monazite , which is found widely distributed worldwide, and bastnasite, found in southern California. It also occurs in the minerals cerite, found in Sweden, and allanite, found in Greenland and New York state. Cerium is the only one of the rare earth metals that can be easily separated from the others. Cerium melts at 798° C (1468° F), boils at about 3443° C (about 6229° F), and has a specific gravity of 6.77; the el...