| The oxide of gadolinium, gadolinia, was separated by Marignac in 1880 and it was Lecoq de Boisbaudran who independently isolated the element from Mosander’s “yttria” in 1886. Gadolinium is found in several minerals. The two of commercial importance are monazite and bastnasite. Seventeen (17) isotopes of gadolinium are now recognised, seven (7) of which occur naturally. The metal may be prepared the reduction of the anhydrous fluoride with metallic calcium. The metal has a silvery white appearance with a metallic lustre. It is ductile and malleable. Gadolinium metal is ferromagnetic. Gadolinium has two temperature dependant crystal structures, at room temperature it crystallises in the hexagonal, close-packed a form. Upon heating to 1235°C, a gadolinium transforms into the b form, which has a body-centred cubic structure. Gadolinium metal is relatively stable in dry air, however in moist air it tarnishes with and forms a loose oxide film, which spalls off, and exposes fresh metal to oxidation. In water it reacts slowly and is soluble in dilute acid. Gadolinium has the highest thermal neutron capture cross-section of any know element (49 000 barns.). However, gadolinium has a very fast burnout rate and for this reason has limited use as a nuclear control rod material. | 
Goodfellow
