It is still dark when Solange leaves home at 5:00am for her job in the mines of eastern Congo, where she digs by hand for a dull black metallic ore called columbite-tantalite.

You might never have heard of it, but this ore — known as coltan for short — contains a key metal used in the manufacture of electronic circuit boards that power smartphones, game consoles and computers.

But the story of coltan is about much more than mining profits and technological wonder. It is also a story of exploitation.

Congo's black gold

Years of violence and political conflict across the Democratic Republic of Congo have made its vast mineral wealth an attractive revenue raiser — and rebel groups will do whatever it takes to control supply.

As a result, the coltan mining industry, and the prized metal tantalum extracted from it, is a "conflict mineral", closely linked to a range of human rights abuses in a similar way that Africa's so-called blood diamonds are also sold to fund conflict.

Years of violence and political conflict across the Democratic Republic of Congo have made its vast mineral wealth an attractive revenue raiser (file photo). ( Reuters: Goran Tomasevic )

Children like Solange are the first to pay the price of the coltan trade. Many start working from as young as seven years old.

Solange started work in the mines when she was just 11. By 14, she was married. Now 17, Solange is already a widow and the mother of two little boys aged one and two.

There are 53 workers at the mine site in North Kivu, including 32 girls like Solange. When Solange was hired, she was assigned to work alongside a team of 18 men, digging coltan with them all day and eating with them at night.

"I got used to them. I was not ashamed like other women," she says.

Most of the mine workers come from poor families and have little education. They have few other options for earning a living.

There are 53 workers at the mine site in North Kivu, including 32 girls like Solange. ( Supplied: Esdras Tsongo )

Compared with the others on her team, Solange — who completed high school and won a place at university — is considered highly educated.

But she never had a chance to finish her university degree.

"As I was the eldest daughter I took responsibility for my little brothers," she says. "I started working in the mines because my parents could not afford my university fees."

Being the victim of poverty and child labour is not the worst of her story. Solange's clear intelligence, comparatively high education and work ethic, does her no favours here.

She was envied by her co-workers, and ultimately abused.

When her husband Dieudonne died in a car accident soon after her first child was born, there was no-one to look out for her.

Vulnerable, alone and with a young baby to care for, Solange was just 15 when she says her team leader began demanding sex.

"He told me if I didn't have sex with him he would drive me out of the mine zone," she says. Solange knew her parents relied on her salary to help the family survive.

At first she refused. But in return, Solange's boss made her job more difficult — assigning her on daily 10km walks to sell coltan in a nearby town.

Solange knew she was being punished for refusing her boss's advances. She was exhausted and felt threatened. Her young child was suffering. "I was scared," she says.

The coltan mine site in the mining area of Nyagisenyi, North Kivu, Democratic Republic of Congo ( Supplied: Esdras Tsongo )

Eventually, the pressure became too much. Solange agreed to sleep with her boss in return for being moved to a higher-paying and less-physically demanding job. After a week, Solange's boss promoted her to team leader.

"I made a lot more money when the chief gave me this opportunity," she says. "But I was like a sex slave to my boss and I had a child with him."

Solange says she felt emotionally tortured by the deal she had struck.

"It was hard. My life in the mines was good but I was sexually abused by my boss almost every week," she says. "I could not give up the job because I needed the money to support my children and my parents."

As the months wore on, she began to question her decision. Recently, she has left the relationship with her boss and returned to the hard work of mining by hand.

"I no longer receive a lot of money but I also no longer needed to accept my boss's sexual advances," she says.

Solange weeps as she explains that for a wage of just $US21 a week, she works constantly with no day off.

"It's really hard work, but here we have no other work that can pay us this amount a day," she says. "I have to stay in this job."

Despite her low salary and long hours, Solange is still better off than many other Congolese, with most living on less than $US1.90 a day.

Exploitation

Amnesty International is concerned the smartphone industry is rife with the suffering of teenagers like Solange, and says global tech companies must do more to clean up the supply of mineral resources used in electronics manufacturing.

Every month, foreign buyers representing global technology manufacturers arrive in the DRC to buy coltan from state-run mining cooperatives, meaning tantalum dug by children like Solange almost inevitably ends up in the global supply.

Attempts are made to ensure coltan is ethically sourced, but it is difficult to manage.

When supply from countries like DRC is mixed with ethically sourced minerals, it is possible to disguise coltan's origins and make it more difficult for manufacturers to be identified for using resources sourced off the back of human rights abuse.

Francine Uwimana, 19, also works in the Nyagisenyi mining area. ( Supplied: Esdras Tsongo )

Solange is not the only woman to have been abused while working in the mines but most are too ashamed, or fearful of losing the work, to speak up.

With limited education, Solange believes many of her female peers have trouble understanding and explaining what they have been through and instead, suffer alone.

The long and busy days, coupled with a large workforce, means close friendships are hard to form, Solange says.

"I don't want to die working here," she says.

"I hope one day I can have my own business. But for now I must find a way to survive this mining life."