Sotheby’s will auction off one of the world’s rarest stones on November 11th, a rare vivid blue diamond nicknamed the Blue Moon Diamond. The 12.03 carat, internally flawless stone was named for the saying “once in a blue moon” for its particularly deep color.

“While any diamond with natural blue coloration is a rare discovery, some are so exceptional that they emerge only once in a lifetime. The Blue Moon Diamond is one of those remarkable occurrences,” said the Gemological Institute of America of the diamond, calling the color so notable that it was “likely to have never before been seen within such a large diamond or any gemstone.”

The stone is estimated to sell for $35 to $55 million. The current record for a blue diamond is $32 million; a 9.75 carat stone known as “The Zoe Diamond” sold in 2014.