We play war games on machines that fuel wars. Never mind the supposedly corrupting software – the hardware has a direct relationship to the deaths of millions. We talk of the immateriality of internet culture; all that is solid melts into air, into the cloud. But what coltan represents is the hidden material world that fuels this cloud and the enormous human suffering wrought in the process. Just as there are unseen mainframes full of personal photos, love letters and savings, so are there tiny chunks of black metallic rock being pulled out of the mud that will one day run a carefully constructed computer model of a real-looking corpse on L.A. Noire.