Platinum group (Pt, Pd, Ru, Rh, Os, Ir)

Six extremely rare metals that clean your car exhaust and turbocharge industrial chemistry, but which are also the focus of a violent power struggle in South Africa.

Presenter Laurence Knight heads to Johnson Matthey, a company that pioneered the car catalytic converter in the 1970s, to find out how they work and to watch the kind of emissions test that Volkswagen cheated.

Andrea Sella of University College London makes a piece of one of these precious metals pop, and explains why platinum crucibles are the bees knees of nineteenth century chemistry.

And the BBC's Vumani Mkhize reports from brutal fight between two unions for supremacy over what is the world's biggest source of platinum group metals.

(Picture: Car exhaust; Credit: ruigsantos/Thinkstock)