RAPAPORT... Christie's will offer a 228.31-carat diamond that could fetch up to $30 million at its upcoming Geneva sale.The pear-shaped, G-color, VS1-clarity stone, called The Rock, is the largest white diamond ever to appear at auction, Christie's said Friday. The previous record for a white diamond was set by a 163.41-carat stone the auction house sold in Geneva for $33.7 million in 2017, Christie's explained. The Rock is also the biggest existing D- to Z-color diamond of its shape the Gemological Institute of America (GIA) has ever graded. The diamond was mined and polished in South Africa more than 20 years ago, Christie's noted. It will headline the auction house's May 11 Magnificent Jewels sale."The Rock will join the very best of legendary gemstones which have passed through Christie's global salerooms since 1766," said Rahul Kadakia, international head of jewelry at Christie's. "The market for diamonds is particularly vibrant and we are confident that this sensational gemstone will capture the attention of collectors across the globe this spring season."Christie's will exhibit The Rock at its Dubai showroom from March 26 to 29, before bringing it to Taipei, Taiwan, and New York. It will then be on display in Geneva from May 6 to May 11 prior to the sale.Image: The 228.31-carat diamond. (Christie's)