MUZO, Colombia — Although he has helped transform Colombia's emerald industry, long a source of violence and environmental damage, former U.S. diplomat Charles Burgess admits that he got into the business on a whim.

"I don't have a mining background," he told NPR during a recent tour of the mine he runs near the town of Muzo deep in the Andes Mountains. "I never in my wildest imagination thought I'd be working in any sort of business like this. But it's been fascinating."

Burgess, 67, is president of the Muzo Companies Colombia that mine and export 85% of Colombia's emeralds, helping to make the country the world's largest producer of high-quality emeralds.

Most of the green gemstones are extracted from a maze of shafts that extend more than a half-mile underground. The entrance to the mine resembles a road tunnel allowing heavy machinery to pull out rocks and debris instead of having miners push it all out in hand carts.

Massive hoses feed fresh air into the mine, while monitors keep tabs on air quality and pumps remove excess water from the mine floor. Telephone and internet services have been installed in case of emergencies.

"This is just a more modern way of running a mine," Burgess says, adding that there have been no fatal accidents here since Muzo Companies bought the mine in 2012.

Colombia's emerald industry used to be far more dangerous, with frequent explosions inside the mines — and gun battles on the outside.

The business was controlled by family clans, some of which formed private armies and had ties to cocaine traffickers who used the emerald industry to launder money, says Petrit Baquero, the author of a book on Colombia's emerald mines. Disputes for control over the industry set off what was known as a "green war" in the late 1980s that killed about 3,500 people.

"There was an influx of fortune-seekers and violent criminals with very little government presence in the region," Baquero says. "It was the law of the jungle."

Ramiro Melo, a 58-year-old emerald miner from Muzo, says: "It was a scary time because these people would kill whoever they wanted."

Back then, he said, miners worked as unpaid prospectors with their bosses giving them just a tiny sliver of the profits when they found emeralds.

"It was like the lottery. You could go for three months without earning a peso," Melo says. "That was the life of an emerald miner."

The violence scared away Colombian investors while several mine owners were imprisoned in the U.S. on drug charges.

In addition, the man known as Colombia's "emerald czar," Victor Carranza, who had survived two assassination attempts as well as efforts to prosecute him for alleged ties to paramilitary death squads, was dying of cancer and wanted to sell out.

"All these guys knew they were depleting their resources and that they couldn't keep going," says Guillermo Galvis, president of the Colombian Emerald Exporters Association. "They were begging me to find foreign investors."

Enter Burgess, a Florida native and Marine Corps veteran who served as a political officer at U.S. embassies in Colombia and several other Latin American nations before retiring in 2009.

While in Colombia, he had become friends with a Roman Catholic bishop who had helped arrange a cease-fire between warring gangs in the emerald zone. With the industry sagging, Burgess agreed to help find foreign financing. Huge sums were needed because the gems were getting harder to find while open-pit mines, that contaminated rivers and caused deforestation, were being phased out for underground mining.

"If you don't improve your technology, it becomes more and more difficult to find emeralds," Galvis says. "You have to go deep, and underground mining involves a lot of resources."

Burgess helped put together a group of Houston-based investors, who in 2012, bought Carranza's mine, Colombia's largest, and put the former diplomat in charge of running it.

"The idea was to fundamentally change the industry," Burgess says. "Instead of seeing this as treasure hunting, we want people to see this as a job and a career."

Little by little, that's what's been happening.

The open pits are gone, replaced by tunnels. Much of the mine Burgess oversees is now mechanized. During a recent tour, geologist Camilo Pinzón uses a pickaxe to open a vein of white calcite rock that's streaked with green — the telltale sign of emeralds. He then places the rocks into a bag to be sent to a laboratory for analysis.

Depending on the quality, he quips, "they could be invaluable, or they could be worth the price of a piece of candy."

Pinzón and other mine employees now receive regular salaries transferred directly into their bank accounts. Women used to be considered bad luck and were largely kept out of the mines but now they are everywhere, says María Fernanda Cardona, 27, a geologist who has been working for the Muzo Companies for the past year.

Dressed in rubber boots and fueled with coffee, Burgess can often be found inspecting tunnels and meeting with engineers and local government officials. He's had to fire miners for stealing emeralds. After one major discovery, word leaked out and suddenly 5,000 people descended on the mine hoping for a piece of the action, until they were removed by police and army troops.

Now, however, the emerald mining region is largely peaceful. Last year, the Muzo Companies Colombia exported about $128 million in emeralds. The United States is the largest importer, according to Galvis.

This area was first mined by Indigenous groups long before the Spanish Conquest, yet it keeps yielding emeralds.

"It's just how it is, it's just the geology," Burgess says. "The potential here is virtually unlimited."