Massive opal sells for nearly $144K at Alaska auctionJUNEAU, Alaska (AP) – A gemstone, billed as one of the largest gem-quality opals in existence, was sold for $143,750 at auction in Alaska on February 20. The opal, dubbed the Americus Australis, weighs more than 11,800 carats, according to the auction house Alaska Premier Auctions & Appraisals. It also has a long history.