Atomic Mass: 138.90547 amu
Melting Point: 920 °C
Boiling Point: 3464 °C
Well we've all been very excited, or maybe it's just me, to learn about Lanthanum. It's our big chance to figure out what the "lanthanide series" is all about! The Lanthanide elements, see, are the ones numbered from 57 to 71 that, along with their cousins the Actinides (Elements 89-103, many of which are totally fakey), are usually plucked out of the Periodic Table and listed seperately underneath. It turns out, however, that this is just a convention used to keep the table pleasantly rectangular. They should properly just fit right into the rest of the periodic table, which properly rendered is much more horizontal than we usually think of it.
This is not to say that the various Lanthanides have nothing in common. They do! For one thing, they are all basically silvery metals, but then what isn't? Their similarities go well beyond this, though, to the point where it was long thought by nineteenth century chemists that all the Lanthanides were just Lanthanum, and only later realized that a whole bunch of related elements were all hanging out together. To foray into the frontiers of my understanding, what we've got here is a series of elements with full "4f electron shells," all of which tend to form "trivalent cations" with a charge of +3. What I think this means is that elemental Lanthanides are electron-hungry and liable to hook up with just about any other reactive element it runs into that is willing to share an electron for the night, or for long stretches of geologic time.
Well, this would certainly explain why they were historically so hard to find and tell apart. Take Element of the Month Lanthanum, for instance. It was "discovered" in 1839 by one of the brainy Swedes, but "isolated in a relatively pure form" only in 1923. This kind of elusiveness is why Lanthanides (along with a few Periodic neighbors) are sometimes called the "rare earths" despite that they aren't especially rare or especially earthy. Hard-core chemistry people distain this term, I have read, so use it sparingly at the faculty mixer unless you are solidly ensconced in the humanities corner.
Human use of Lanthanum, either in compounds or alloys, was pretty esoteric until recently: arc lamps, optical glass, catalytic processes, and as a method of removing phosphates either from swimming pools or the bodies of people experiencing renal failure. There's a big Lanthanum boom on recently, though, due to its use in the batteries that power hybrid automobiles. Apparently if you've got a Prius, you're driving around with as much Lanthanum under your trunk as the mass of three average-sized cats. That's a lot, but there are some who think that more hybrid efficiency is going to require more and more Lanthanum, until a good hybrid is going to be packing five or six cat-equivalents of the stuff! I'd suggest buying up Lanthanum futures, but probably other people have already beat you to it.