One evening in 2014 , a police officer in Kolwezi, a dusty mining city of a half-million people in the southern Democratic Republic of Congo, decided that his family needed a new latrine. He picked up a shovel and started digging a pit in his yard and soon stood transfixed at the shimmering black dirt he’d unearthed: Before him was a pile of cobalt, one of the world’s most important minerals.

Cobalt is an essential component of rechargeable batteries in cars and mobile phones, and Congo is by far the world’s largest producer, with about half of all known reserves. In Kolwezi, the cobalt is often found with vast deposits of copper: After a rainstorm, some of the ground in the city turns as green as the Statue of Liberty. With the electronics boom worldwide, demand for both minerals has exploded.

In the days that followed the policeman’s discovery, he began digging up his living room, his bathroom, his bedroom, his kitchen. Within weeks, his neighbors followed suit. By mid-2015, when I started visiting that area of Kolwezi, known as Kasulo, the place looked as if it had been bombed.

Kasulo was once a quiet hillside neighborhood, home to the families of the cooks and cleaners, mechanics and drivers who worked for the mining industry. Now its small brick and concrete houses were crumbling and the streets were pockmarked with cavernous holes.