Rio Tinto to Book $14 Billion Charge; C.E.O. Steps Down

``Two expensive acquisitions have come at a steep price for Rio Tinto, the Anglo-Australian mining giant. The company, the world's second-largest mining company after BHP Billiton, said on Thursday that it was taking a $14 billion write-down on the value of aluminum and coal mining assets -- a huge amount that came as a surprise to some analysts and investors.''