Your smartphone contains about one dollar’s worth of gold, buried in its circuitry. Not a lot. But it could have been bought from an illegal and exploitative mining operation in Colombia.

Gold is one of the major conflict resources, along with tin, tungsten, and tantalum. These are the precious commodities often found in the world’s poorest countries and mined under threat of violence from armies and militia. The problem is well documented in countries like the Democratic Republic of Congo and the Central African Republic.

But a new report from Bloomberg suggests that the same problem can be found a little closer to home, in the illegal gold mines of Colombia. The report claims that “85 percent of the 59 tons of gold produced last year in Colombia comes from operations without government licenses or environmental permits,” adding that many of the mines are “under the control of Marxist guerrillas or drug traffickers.”

Despite independent checks, large companies from phone manufacturers to automakers likely have such gold in their supply chains. The illegal mines are certainly profitable at any rate: Colombian police claim that rebels make more money from gold than they do from cocaine.

There are some initiatives that attempt to ensure that materials used in consumer electronics are conflict-free. Large companies like Apple certainly strive to, but they struggle to chase supplies all the way to the ground. Perhaps the most impressive is a company called Fairphone, which makes ethical Android handsets built from materials procured via heavily vetted supply chains. Its handsets use only Fairtrade-certified gold.

Until that stops being a niche offering, gold and other materials will continue to be mined in dangerous and exploitative ways. And for now, we all carry a little reminder of that problem around with us in our pockets.

(Read more: Bloomberg, “The Human Cost of the Lithium Battery Revolution”)