Jeopardy! category: CHEMICAL ELEMENT PAIRS (10-2-2015)
$1200 clue: Symbols Os & Ir, they are the 2 densest naturally occurring elements
The gist: They’re also two of the elements that meteors have in much higher concentrations than Earth does. As a result, osmium and iridium, the latter more famously, play big parts in geology and the chronology of the Earth, serving as delineation marks for several catastrophic impacts. Perhaps the most famous is the impact proposed in the Alvarez hypothesis, which claims, probably rightly, that a meteor impact at the Chicxulub Crater in Yucatan, Mexico, caused the global climatic changes that eventually killed of the non-avian dinosaurs. The father-and-son team based their initial hypothesis on the elevated levels of iridium they found in the stratum that divides the dinosaur age from the mammalian age – osmium, being much less prominent, didn’t play a great role in the hypothesis, but rest assured it’s there as well.
Aside from being the densest, the two are also in the top three rarest naturally-occurring elements (osmium at the top of list, with rhodium in between the two). In fact, osmium and iridium can be found as the two elements in the alloys osmiridium or iridosmium, depending on the ratio between the two metals. Both the metals are found naturally in igneous rock as well as in impact layers, but today they are most commonly produced as byproducts in the smelting of more common metals like nickel and copper. They are also both very resistant to corrosion and have high melting points, and so are used in a variety of industrial applications, from the production of the nibs in ballpoint pens (since they see so much wear for their size) to staining in electron microscopy.
The clue: Osmium and Iridium don’t have the toughest atomic symbols of them all. If you have some idea in the back of your mind that there are in fact two elements with those names, you may be able to recall them just from seeing their first two letters, which seems much more likely to me than actually knowing the two densest naturally occurring metals off the top of one’s head. But they’re also not elements most of us encounter very often in daily life, so the $1200 spot is a fine place for them.
In Jeopardy!: The two show up in three clues together in the J!Archive, including this one. One of them asks for the metal group they’re in (platinum) while the other asks what two elements osmiridium is made of (another clues that’s really about alphabetical/spelling/phonetic hints and not about knowing the science behind it). Osmium has only appeared in these three clues, but iridium is in another 14. Four of them are about its role in researching the demise of the dinosaurs, and two mention its high resistance to corrosion (while also giving its symbol). It also had its very own DJ! category in a 2002 game. Check it out.