NEW YORK: A pink diamond the size of a postage stamp is going on the auction block and it's estimated to bring as much as $28 million. The 16.08-carat gem could set a record for a cushion-shaped fancy vivid pink diamond when it's offered at Christie's in Geneva on November 10. The auction house says it's the largest diamond of its kind to come to auction. A smaller, 8.72-carat pink diamond of the same shape and fancy vivid pink grade sold for $15.9 million at auction in May. Fancy vivid pink means the hue is of the purest and strongest saturation. Christie's says the seller purchased it 10 years ago as an investment. A 25-carat emerald-cut pink diamond holds the auction record for any diamond. It sold for $46 million in 2010.