A diamond ring is seen on display at Serendip Jewellers in the Hatton Garden Jewellery Emporium in London April 2, 2012. A stock market flotation is likely to top the list of options when Rio Tinto reviews the future of its diamond business, as a shortage of heavyweight buyers prompts the miner to turn instead to funds betting on Asia's appetite for luxury. The Anglo-Australian mining giant could add to the allure of an initial public offering by first seeking to merge its diamond operation with another that is on the block from rival BHP Billiton, bankers and analysts said. Picture taken April 2, 2012. To match Story US-DIAMONDS/ REUTERS/Luke MacGregor (BRITAIN - Tags: BUSINESS)