Gadolinium is a metallic chemical element that is classified in the rare earth metals. Most of the world's supply is found in various minerals, which are processed to extract usable elements; this element is extremely rare in a pure form because of its reactivity and vulnerability to corrosion. It has a number of industrial uses which ensure that there is a fairly steady demand for it. Consumers rarely interact directly with gadolinium, although they may own or use products that integrate this element.
In a pure form, gadolinium is a shiny white metal with a crystalline structure. It is extremely malleable, and it also reacts weakly with water. When it is exposed to moist air, it forms a distinctive flaky crust that will slough off to expose the underlying metal to the elements. The pure metal can be stored in an sealed container or in mineral oil so that this crust does not form and ruin it. On the periodic table of elements, it is identified with the atomic number 64 and the symbol Gd.
In medicine, gadolinium is used as a contrast agent for some medical imaging, and it also appears in some imaging equipment, such as MRI machines. The element is also used in a wide range of metal alloys, and it appears in some nuclear reactors as well. It is also used in the manufacture of synthetic gemstones, and it has some unusual magnetic properties which are sometimes harnessed in scientific experiments. At room temperature, gadolinium is paramagnetic, while it becomes ferromagnetic as it cools.
The discovery of gadolinium is credited to Jean de Marignac, who observed its characteristic spectroscopic signature in 1880. It took several more years for a French chemist to successfully isolate an oxide of the element, which was named for Johan Gadolin, a prominent Finnish scientist. Gadolinite is also named for Gadolin, although this mineral contains little to no gadolinium, which can be confusing.
Gadolinium should be handled carefully, because it can be toxic, like other rare earth elements. The precise toxicity of it is unknown, but it's safe to say that people should probably avoid inhaling fumes and particles from the metal while it is being worked, and it shouldn't be ingested either. Its medical use has been linked with complications in people with kidney disease, so medical professionals tend to use other contrast agents in imaging studies on people with kidney problems.