(IDEX Online) - Inmates at an Indian jail are cutting and polishing diamonds behind bars.It's common for prisoners to work in laundries or kitchens, in sewing or agriculture. But those at Lajpore Central Jail, in Surat, are believed to be the only ones in the world working with diamonds.Just over 100 of the prison's 3,000 inmates work at the polishing unit, according to the Times of India (ToI).They produce 25,000 small diamonds a month between them, and earn up to $240 (Rs20,000) a month.They're allowed to keep 10 per cent for personal expenses in prison and send the remainder to their families.Some of the men were already diamond artisans, others have learned the skills while inside."I have learned diamond polishing after I was lodged in the jail 11 months ago," he told ToI. "I hope to keep working as a polisher even when I am out of jail." Pic courtesy Gujurat Prisons, shows Lajpore Central Jail