An ultra-rare 3.15 ct. red diamond will highlight Christie’s upcoming Magnificent Jewels Auction, which will be held in New York City on Dec. 7.

The circular-cut fancy reddish orange gem is the largest reddish orange diamond ever graded by the Gemological Institute of America, and the largest to appear at auction.

Red and orange fancy-colored diamonds are considered among the rarest and most sought-after of fancy colored diamonds. Scientists are not sure what causes their color. Very few red diamonds over 1 ct. are known to exist. The largest known red—a circular-cut 5.03 fancy dark red—now resides in the permanent collection of the Smithsonian Institution in Washington, D.C.

The stone has SI2 clarity, excellent symmetry and polish, and is estimated to fetch between $700,000 and $1.2 million.

Other auction highlights:

• The sale will also feature another notable piece: a Graff-designed ring with a 50 ct. rectangular-cut D-color center stone, which the auction house describes as “potentially internally flawless.” Its current clarity grade is VVS2. It carries a $7 million–$10 million estimate.

• Christie’s is also selling a three-stone Colombian emerald ring, featuring gems of 8.51, 4.04, and 3.94 cts. It carries a $475,000-$550,000 estimate.

Click here for the complete catalog.

JCK