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: Is It Really Hard to Crush a Diamond?
At some point in school, I had to learn the Mohs scale of hardness, which assigns numerical values to ten different minerals in order of hardness. I've forgotten most of the actual minerals, though. 1 is talc, I think, which is as soft as rock ever gets, unless you count 1970s AM radio. I don't remember any of the others. Except 10! Nobody ever forgets 10. 10 is diamond. 10 is as hard as rock can get. 10 is Black Sabbath or Cannibal Corpse.
It's the one thing everyone knows about diamonds: nothing can scratch them. Detectives rub them onto window glass to test their authenticity. Scientists synthesize them in labs to make indestructible industrial parts. As Benjamin Franklin once said, "There are three things extremely hard: steel, a diamond, and to know one's self." So it would be incredibly hard to crush a diamond, right? You'd need, like, another diamond, or a hydraulic press, or the fires of Mount Doom or something? Not at all. In fact, you can break a diamond just by whacking it with a hammer.
The crux of this misconception is the meaning of "hardness" in the Mohs scale. Geologist Friedrich Mohs was being a little cagey there; what his scale actually measures is scratch resistance, a test that science has been using to compare mineral hardness for at least 2,300 years, as far back as the Greek philosopher Theophrastus. But the scratch test doesn't evaluate a mineral's toughness or tenacity. The simple crystalline structure of diamonds means that they cleave very easily, so their fracture toughness is only about 290 pounds per square inch. That's not bad for a gemstone but can't really compete with modern engineering materials. Long story short: if you're building some kind of impregnable space fortress, use steel or titanium alloy, not diamonds.
Quick Quiz: Corundum, the second hardest mineral on the Mohs scale, is called "ruby" if it's red. If it's any other color, what kind of gemstone is it?
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.