One of the most remarkable things about diamonds is that they exist in nearly every shade of the rainbow. While colored diamonds are an unusual natural occurrence as a whole, the rarest of them all are red. 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 a whopping 5.11 carats is unearthed, it is bound to gain international attention. Even though 5.11 carats may not seem very large, the Moussaieff Red diamond is actually the largest fancy red stone ever graded by the Gemological Institute of America.

Moussaieff Red DiamondMoussaieff Red Diamond

A cut above the rest

According to Internet Stones, a farmer in Brazil found the deep red diamond in the mid-'90s, and in the rough, it weighed an impressive 13.90 carats. The source noted that it's likely the stone was formed in the mining area's alluvial deposits. It was then bought by the William Goldberg Diamond Corporation of New York, which is known for possessing remarkable stones like the Guinea Star and the Premier Rose. After the Goldberg Corporation cut the stone into a triangular brilliant cut, also known as a trillion or trilliant cut, it lost 8.79 carats in the process - but the result of the transformation was stunning. The diamond was named the Red Shield, until Moussaieff Jewelers acquired it in the early 2000s for around $8 million.

According to Diamond News, expert gemologist Michael Hing, who saw the diamond in person around that time, was taken aback by its beauty.

"It's a really surprising cranberry color, quite unlike any other diamond I've ever seen," Hing said, as quoted by the source.

The Moussaieff Red on display twice at the Natural History Museum of the Smithsonian Institution in Washington, D.C. The stunning stone was featured as part of the "Splendor of Diamonds" Exhibition June 2 to Sept. 30, 2003, alongside other legendary gems like the Millennium Star, the Pumpkin diamond, the Heart of Eternity and the Ocean Dream. Later, it was included in another exhibition from July 8, 2005 through Feb. 26, 2006, which also featured the De Beers Millennium Star, The Steinmetz Pink and the Aurora Collection, a set of 296 naturally colored diamonds weighing in a total of 267.45 carats.

Uncommon characteristics

How does a red diamond get its breathtaking hue? The Cape Town Diamond Museum explained that nitrogen or boron is responsible for other diamond colors, red diamonds are rather different. Like colorless stones, they are made of pure carbon. So instead of the presence of impurities, it's a deformation in the atomic makeup of the stone that produces the red color. This structural flaw is called plastic deformation, and it causes light to pass through the lattice and bend in such a way that it reflects the gorgeous ruby-like hue. As with any other colored stone, the more intense the hue, the more rare and valuable it is. The intensity can range from a dark pink diamond to a purplish red one.

What is perhaps most fascinating about red diamonds is that their appearance varies based on the lighting in their surroundings. According to The Cape Town Diamond Museum, fluorescent light is the least complimentary to these stones, while daylight and candlelight bring out their beauty.

The Cape Town Diamond Museum also noted that red diamonds are expected to become even more difficult to come by in the future. As a result, experts predict they will cost double what they do now within just a few years.

Other famous red diamonds

There have been a number of other noteworthy red diamonds throughout history.

Red Diamond from Argyle MineRed Diamond from Argyle Mine
Image via Argyle Diamond Mine

Not much is known about the second-largest red diamond in existence after the Moussaieff. Internet Stones reported that the 5.05-carat emerald-cut stone was found in 1927 in South Africa. While it's thought to have been bought by an anonymous collector, the current location of the unnamed red diamond is a mystery.

After that, the De Young Red is the next-largest gemstone in this hue. Weighing in at 5.03 carats, it is a round brilliant cut and has a slight brownish tint. Because of this misleading hue, Internet Stones noted that it was initially sold as a garnet. Now, the De Young is owned by the Smithsonian Institution's Natural History Museum.

Despite the fact that the Hancock Red diamond, formerly known as the Halphen Red, is only 0.95 carats, it is still rather famous due to its rare purplish red hue. It was purchased by a renowned collector named Warren Hancock in 1956 for $13,500. The stone was later bought for $880,000 in 1987.

Another remarkable gemstone is The Rob Red, a pear-shaped stone that weighs a modest 0.59 carats. What's truly special about this diamond, the Cape Town Diamond Museum explained, is that it boasts VS1 clarity, and the purest and most saturated hue of any red diamond discovered.