The Moussaieff Red Diamond (formerly known as the Red Shield Diamond) is a diamond measuring 5.11 carats (1.022 g) with a triangular brilliant cut (sometimes called a trillion or a trilliant cut), rated in color as Fancy Red by the Gemological Institute of America. It is the world’s largest known red diamond, the rarest of them all.
The Moussaieff Red was discovered by a Brazilian farmer in the Abaetezinho river in 1990, in a region known as Alto Paranaiba. The rough stone weighed 13.9 carats (2.78 g). The diamond was purchased and cut by the William Goldberg Diamond Corp., where it went by its original name, the Red Shield. It was purchased in 2001 or 2002 by Shlomo Moussaieff, an Israeli-born jewelry dealer in London, and is currently owned by Moussaieff Jewellers Ltd.
The Moussaieff Red was displayed in 2003 as part of the Smithsonian Institution’s “The Splendor of Diamonds” exhibit, alongside The De Beers Millennium Star and The Heart of Eternity.
One of the most amazing things about diamonds is that they exist in nearly color. While colored diamonds are an unusual natural occurrence as a whole, the rarest of them all are red diamonds. In fact, according to the Cape Town Diamond Museum, only roughly 20 to 30 true red diamonds have been discovered, and the majority of them are less than 1/2 carat in weight.
As such, these gems also command some of the highest price tags ever set. That is why when a red diamond that weighs over 5 carats is unearthed, it will gain international attention. Even though 5 carats may not be very large, the Moussaieff Red diamond is actually the largest fancy red stone ever graded by the Gemological Institute of America.