'It’s possible that two children died so that you could have that mobile phone,' says Jean-Bertin, a 34-year-old Congolese activist who wants to end the 'absolute silence' around the crimes committed in his country to exploit strategic raw materials like coltan. The Democratic Republic of the Congo (DRC) has at least 64 per cent of worldwide reserves of coltan, the colloquial African name for a dull black ore composed of two minerals, columbite and tantalite.