In a packed Christie’s auction room in Geneva, one could hear a pin drop as two anonymous bidders slugged it out in their quest to own the world’s most exquisite blue diamond. The room in the Four Seasons Hotel des Bergues was filled with multi-millionaire collectors and diamond dealers, listening intently as the bidders, each speaking by phone to a Christie’s representative, took turns adding a few hundred thousand dollars in a tense struggle dragging on for more than half an hour.