Here’s a head-scratcher: Thieves don’t want to steal your car. They just want to saw off your tailpipe and grab the catalytic converter.

The phenomenon is common in Britain, and thousands of reports of catalytic converter heists are popping up in the United States, The Washington Post reports. The reason? Rhodium, a silver-white metal that serves as a cautionary tale about how economics and technology can make commodity prices suddenly soar – and plunge.

Rhodium, it turns out, is highly effective at filtering out a nasty pollutant from car emissions. And it’s in short supply.

In the past three years, prices have skyrocketed from $1,700 to $27,000 an ounce, more than 15 times pricier than gold. And we won’t see a surge in supply anytime soon because rhodium is a byproduct of platinum production, and there’s such a glut of platinum that even high rhodium prices won’t kick-start new production.

But don’t push the rhodium panic button just yet. A decade ago, Western nations fretted about China’s limited bans on exports of rare earth minerals. The doomsayers turned out to be wrong, in part because companies found substitutes. So this time car companies may find a way to retool catalytic converters – or they’ll just start selling more electric vehicles.