Gold tumbled 400 rupees, to 28,000 rupees per ten grams at Delhi's bullion market, today, on heavy selling by stockists, triggered by a weak trend overseas. Silver plunged 1,500 rupees, to 43,100 rupees per kilo, on poor offtake. Silver coins nosedived 2,000 rupees, to 78,000 rupees for buying 100 pieces.In London, gold sank 3.4 per cent, to its lowest in more than 2.5 years, at 1,305 dollars an ounce, after US central bank chairman Ben S. Bernanke said asset purchases may be reduced later this year as the US economy recovers. Silver fell 6.2 per cent, to 20.08 dollars an ounce, the cheapest since September 2010.