'Blue Moon' Diamond Could Fetch $55 Million at Auction

— -- A flawless diamond so rare it gets its name from the expression “once in a blue moon” could fetch as much as $55 million at an auction next week.

The 12.03-carat stone, referred to as “The Blue Moon," will be up for auction Nov. 11 at Sotheby’s “Magnificent Jewels and Noble Jewels” sale in Geneva.

The diamond has “internally flawless clarity and truly outstanding colour,” according to a description from Sotheby’s.

The auction house says the exquisite stone was discovered in January 2014 by the owners of the famous Cullinan Mine in South Africa. The diamond was then purchased by New York-based Cora International and was cut and polished.

The diamond has an estimated value of $35 million to 55 million, according to Sotheby’s.

The auction house says the diamond -– deemed “internally flawless” by the Gemological Institute of America (GIA) -- is the “largest cushion-shaped fancy vivid blue diamond” to ever appear at an auction.