Gadolinium

Description: Gadolinium is silvery-white, malleable and ductile with a metallic luster. Gadolinium crystallizes in the hexagonal, close-packed alpha form at room temperature. When heated to 1235°C, alpha gadolinium changes into beta gadolinium, which has a body-centered cubic structure. In dry air, gadolinium is relatively stable. However, in moist air, it tarnishes and forms a loosely adhering oxide film that falls off, exposing more surface to oxidation. The metal has a slow water reaction and is soluble in dilute acid.
Gadolinium has the greatest thermal neutron capture cross-section of any known element (49,000 barns).

Source: Gadolinium can be found in a variety of minerals, including monazite and bastnasite, both of which are commercially important. With the development of ion-exchange and solvent extraction techniques, the availability and prices of gadolinium and other rare-earth metals have greatly improved. The metal can be produced by reducing anhydrous fluoride with metallic calcium.