(IDEX Online) - An exceptional 119-carat untreated royal blue Burmese sapphire is to be sold by Sotheby's.The auction house says it's the largest sapphire of its kind it has ever offered.The legendary Rockefeller Sapphire, which is half the size, sold for $3m in 2001. The 62.02 carat rectangular step cut stone was bought in 1934 by the billionaire John D. Rockefeller Jr from an Indian Maharaja.The 118.88-ct sapphire (pictured), surrounded by 16.06 carats of pear-shaped diamond, will lead the Magnificent Jewels live sale at Sotheby's Hong Kong on 7 October. Burmese sapphires of notable sizes are extremely rare, says Sotheby's, and untreated gems even more so.Accompanying reports by the SSEF and G?? 1/4 belin labs says: "A natural sapphire from Burma of this size and quality is extremely rare and thus can be considered a true treasure of nature"."We are proud to present an exceedingly exceptional 118.88 carat Burmese 'Royal Blue' sapphire, almost double the size of the Rockefeller Sapphire and the largest sapphire of its kind ever to be offered at Sotheby's," said the auction house.