Iridium

Iridium is a super-hard, super-brittle, silvery-white precious metal that lives pretty much smack dab in the middle of everyone’s high school memorization nightmare: the periodic table (atomic number 77). It’s got an insanely high melting point and it’s ultra resistant to corrosion, which means that, not only is it kinda pretty, but it’s also extremely useful. It can be used to make all kinds of industrial bits and bobs, from airplane spark plugs to brachytherapy tools.

Unfortunately, it’s also extremely rare (on Earth, at least). And that makes it extremely expensive. So even though it hypothetically could be used to make everything from bridges to car parts to industrial chic home décor elements...it’s not. It’s used in small amounts, only when needed, and is combined with other less-rare and expensive metals when possible.