The International Diamond Exchange said Sotheby\'s Hong Kong auction house expects a rare blue diamond to fetch $19 million. IDEX said the auction for the 7.59-carat blue diamond will be held in Oct. 7. \"Since about 2006, 2007, Hong Kong has ranked alongside Geneva and New York as a center for jewelry sales,\" said Quek Chin Yeow, deputy chairman of Sotheby\'s in Asia. \"It is now the third pillar of the global jewelry market,\" Quek said.