The Neodymium Day Thread

As we dig deeper into the periodic table, it’s time to consider the concept of scarcity, which will become important as we get into what I lovingly think of as the weird elements. Elements can be rare in two days: they can be uncommon on the atomic level, or they can be difficult to separate. Gold is a good example of the former; the subjects of today’s threads are the latter.

The rare earth elements closely resemble each other chemically. This is a problem if you’re trying to pull them apart, and it was so much of a problem with the elements neodymium and praseodymium that their discoverer, Carl Mosander, thought he they were one element – didymium. You can see it here, with an atomic weight of 95, on the very first periodic table:


A lot of the elements have names built out of Greek words, and Mosander lucked out a little in that he’d chosen a name that meant “two twins.” (Or, at least, I’m pretty sure it means that.) When didymium was finally pulled apart by Carl Auer von Welsbach, 40 years later, he gave them names that reflected their origin. Praseodymium means “green twin,” and neodymium means “new twin.”

Neodymium, like many elements, can be used to color glass, as in the header image from Wikipedia. Neodymium-glass bulbs simulate daylight at the cost of terrible energy efficiency (element enthusiast Theo Gray hates them). Neodymium glass also does more advanced work in lasers, which is apparently what this US government image represents.


Perhaps the most familiar neodymium application, however, is its use in magnets. Neodymium magnets are incredibly powerful for their size, and are used to read and write hard disk platters.

As for praseodymium, the green twin? Check back tonight!