Atomic Mass: 157.25 amu
Melting Point: 1312 °C
Boiling Point: 3000 °C
Gadolinium is one of the rare earth elements, although remember that real chemists don't like the category of "rare earth elements" and you must not tell them I said so. If you are talking to a real chemist, say that Gadolinium is a "lanthanide," which is also true and means almost the same thing. Gadolinium shares many of the characteristics of its brothers and sisters in the the rare earths. It is not really very rare, for instance, but is so reactive that it is thinly distributed throughout all of nature, rarely occurring in anything but a trace concentration. It never occurs naturally in its elemental state. Like with most rare earths, this shyness made it hard to pin down, and it was not identified as an element until 1886, well after our boy Mendeleev published the mother of all spreadsheets.
Needless to say, it is a silvery-grey metal.
Gadolinium has some interesting properties, the weirdest of which in my book is that it is ferromagnetic -- what you and I think of as "magnetic" -- below 68°F. The implication is that you could use it to make a refrigerator magnet that worked all winter, but automatically triggered a cleanup on the first warm day of spring. Should I patent that? It also has the trippy characteristic of being "magnetocaloric," meaning its temperature increases when it enters a magnetic field. This property can actually be exploited to create a fairly efficient refrigeration system. This might be a viable alternative to the way we currently refrigerate, except that Gadolinium is by far the MOST magnetocaloric material, and it is hard to come by. Simple economics will probably keep you from having seasonal Gadolinium magnets on your Gadolinium magnetocaloric fridge anytime soon.
It also soaks up neutrons pretty well, which makes it useful (but risky, due to its toxicity) in nuclear medicine and a good last-ditch defense in a failing nuclear reactor. It is a good alloy for Iron and Chromium if you want high-temperature workability and corrosion resistance. There are a bunch of niche applications, naturally.
Why is Gadolinium "Gadolinium"? It is ultimately named for the brainy Finnish chemist Johan Gadolin, whom a prominent open-author online encyclopedia describes as "the founder of Finnish chemistry research, as the second holder of the Chair of Chemistry at the Royal Academy of Turku." Can you imagine how that must sound to the FIRST holder of the Chemistry Chair at Turku? Ouch!
Did Gadolin discover Gadolinium? No, he discovered Yttrium. It was Jean Charles Galissard de Marignac cooked up a Gadolinium oxide around 1880, and Paul Émile Lecoq de Boisbaudran who actually produced elemental Gadolinium in 1886. The win is usually given to Marignac, who also discovered Ytterbium. If that seems hard on Boisbaudran, consider that he has the discovery of Gallium, Samarium, and Dysprosium on his resume, and shouldn't be greedy.