Investigations spread over a year in the western Indian state of Gujarat found a pattern of suicides – many shrouded in silence – in the industry that cuts and polishes 90 per cent of gems sold globally, with many workers paid per stone.

A few workers in the industry earn fixed wages – some even up to 100,000 Indian rupees (US$1,450) or more a month – but over 80 per cent of the total workforce earn a piece rate of 1 to 25 rupees for each stone they polish and have no social benefits.

Interviews with diamond unit owners, brokers, labour groups, families and the police revealed nine suicides since last November in the city of Surat, a hub for the trade, and the Saurashtra region where the workers are from.

But experts said this was likely to be just the tip of the iceberg in India, where industry figures show diamond exports surged 70 per cent in the past decade, with no mandatory certification to ensure diamond processing is labour abuse free.

Families are reluctant to blame the diamond business, which employs over 1.5 million men – mainly from drought-prone parts of Saurashtra – for fear of losing work, with few other options.

“Vikram started polishing diamonds when he was 16. He had been struggling to get more work,” Raujibhai’s mother Wasanben, said.

Wasanben said her son was worried about mounting expenses and being unable to find love and marry.

“He earned 6,000 Indian rupees ($90) a month, but we were a family of seven and the money was never enough,” she said.

The skills of Indian polishers, after generations in the industry, and low labour costs ensure major mining firms from De Beers – the world’s largest diamond producer by value – to Russia’s Alrosa get raw diamonds processed in India.

When asked about worker suicides, De Beers – of the Anglo American Plc Group – the world’s second biggest mining company Rio Tinto, and Russia’s Alrosa said they had not encountered any cases in firms to which they sell rough diamonds.

Government officials said workers were paid well and the industry is “positive”, setting up schools, hospitals and giving jobs to relatives of workers who died or committed suicide.

But campaigners said while most big firms have air-conditioned workshops and fixed wages, many smaller outfits have no toilets or ventilation and workers live, eat and sleep in the workshops in slave-like conditions.

Rough diamonds imported to India must be certified ‘conflict-free’ by the Kimberley Process scheme to ensure they have not been used to fund civil wars and are free of human rights abuse, not so called “blood diamonds”. KP members account for about 99.8 per cent of global production of rough diamonds.

But certification of cut and polished diamonds given by the global non-profit Responsible Jewellery Council (RJC) is optional.

Only about 90 firms from about 15,000 big and small diamond companies in Gujarat are certified RJC members. About 30 are authorised buyers of rough diamonds from De Beers that binds them to follow a set of labour rules.

But no one is pushing companies for certification of processed diamonds.

The highest number of more than 5,000 suicides reported in Surat city since 2010 were in areas where diamond workers live, police data the Surat police shows.

In Surat, the Thomson Reuters Foundation analysed the suicides of 23 men between January and April and found six cases of diamond workers who had hanged themselves or drank poison. It found three similar cases in the Saurashtra region.

Police officer Ashish Dodiya this year investigated the suicides of two diamond workers in their early twenties who drank poison.

Dodiya dismissed a link between the deaths and work in the cases he investigated.

“They didn’t die because of the diamond business. There are more cases of diamond worker suicides because of their high numbers in this area,” he said.

Other police officers stationed in the area where diamond workers live in Surat did see a link between the suicide cases they investigated and diamond work.

Some workers said they go without wages for at least two months every year when business is slow and they have to borrow money to make ends meet.

Ramesh Ziliriya, who set up a diamond labour association in Rajkot in 2013 to protect workers rights, said while debt bondage and child labour may be a thing of the past in the diamond industry, “slavery and suppression continues”.

“Workers do not protest their low wages as they fear losing their jobs,” the former gem polisher said.

At the Sri Diamond Worker Union in Surat, Mukeshbhai Waljibhai Kanjaria sifts through the letters he has written to state authorities about the problems diamond workers face.

“Earlier, a worker would polish 50 diamonds for, say, eight rupees a piece,” said Kanjaria, the union president.

“Now there are machines and he can polish 500 diamonds in one day, but his earnings have remained the same.”

Kanjaria said workers lack social benefits that other factory workers get, like pensions and subsidised medical care.

But labour officials in Gujarat said diamond industry workers earn more than the minimum wage of 8,300 rupees a month.

“They are not interested in social security as it involves paperwork and both workers and their employers are in most cases illiterate,” said Ashish Gandhi, assistant labour commissioner.

Diamonds processed in Surat are sold to jewellery makers in a bazaar, but nearly 90 per cent are couriered to one of the world’s largest diamond bourses in Mumbai, and then exported.

Jean-Marc Lieberherr, head of the Belgium-based Diamond Producers Association which aims to encourage best practice in the industry, said major mining companies were making a real effort to ensure workers were not exploited.

Hong Kong’s Chow Tai Fook – that most Indian diamond polishing units supply diamonds to – said it buys gems only from those companies that comply with norms set by De Beers and the RJC.