What makes gold so valuable, why is it golden and why is it the only elelment that makes a good currency? In chemical terms it is virtually useless. Justin Rowlatt talks to one of the world's biggest manufacturers of mobile phones about how you can recover the gold in your handset and learns how little gold there actually is. Find out more in the latest in our series examining the world economy from the perspective of the building blocks of the universe - the chemical elements.