Thanks to the hard work of the Association of American State Geologists, the second week of October has been officially declared "Earth Science Week" every year since 1998. So we decided to have Jeopardy!'s rarest gem, Ken Jennings, school us on the hardest rock of them all: diamonds. Are they really forever? Are they a girl's best friend? Let's shed the cold, hard light of 10-carat truth onto some of these semiprecious superstitions.
The Debunker: Do Diamonds Come from Coal?
It's one of Superman's best tricks: hold a lump of coal in his soft, supple Kryptonian hands and casually compress it into a beautiful diamond. Lois Lane swoons. We nod appreciatively, dimly remembering from junior high that this is possible because diamonds are made of carbon, the same element that forms coal. Science!
It's true that diamonds and coal are both largely carbon, but that doesn't mean the diamond jewelry in a mall display case was once coal. Diamonds formed billions of years ago, long before the dead remains of trees and ferns from prehistoric swamps decayed and compacted into coal. In 1989, scientists found tiny little nanodiamonds in meteorites for the first time, proving that diamonds don't need plant matter to form at all. Even Superman wouldn't be able to do much jewelry-wise with coal, which contains far too many impurities to make a very pretty diamond. By weight, as much as half of a lump of coal can be hydrogen, oxygen, nitrogen, and sulfur.
So how did your mom's diamond earrings form? It all happened in the Earth's mantle, perhaps 100 miles below the deepest coal seam. Carbon trapped in the rock there was squeezed into a tight crystalline structure by temperatures of thousands of degrees and extraordinary pressure, around 725,000 pounds per square inch. Volcanic eruptions then brought them to the Earth's surface, where geologists and fortune-hunters look for them in telltale chunks of cooled magma, an igneous rock called kimberlite. So you don't need coal to get a diamond—just a lot of disposable income.
Quick Quiz: What title Disney animated character turns out to be the "diamond in the rough" prophesied by destiny?
Ken Jennings is the author of eleven books, most recently his Junior Genius Guides, Because I Said So!, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at ken-jennings.com or on Twitter as @KenJennings.