Argyle diamonds
The Argyle Everglow is a 2.11-carat radiant shaped Fancy Red diamond. This Fancy Red diamond is the one of largest of its kind to have ever been found.
Argyle diamonds
These "hero" diamonds include two Fancy red, a Fancy Purple-Pink, a Fancy Deep Pink diamond and a Fancy Deep Gray-Violet diamond.
Argyle diamonds
The Argyle Everglow, a 2.11 carat radiant shaped Fancy Red, will be the highlight of the sale.
Argyle diamonds
The October sale will include five "hero" diamonds selected for their unique beauty.
Argyle diamonds
The 2.42 carat Fancy Purple-Pink Argyle Avaline and the 1.14 carat Fancy Red Argyle Isla.
Argyle diamonds
The 2017 Argyle Pink Diamonds Tender will offer a choice of 58 diamonds weighing a total of 49.39 carats.
Courtesy Argyle Pink Diamonds
Scroll through the gallery for record-breaking diamonds. Last year, new auction records and high-profile sales suggested that demand for the world's rarest and most unusually-colored stones has never been greater.
Courtesy Argyle Pink Diamonds
"Diamonds: Rare Brilliance," an exhibition at the Natural History Museum of Los Angeles County, highlighted four beautiful stones, including the Argyle Violet, owned by L.J. West Diamonds Inc. of New York.
Courtesy Brian Lazar
The Juliet Pink from South Africa is also from L.J. West. This rare Fancy Intense Pink weighs whopping 30 carats and is set in a necklace.
Courtesy Aaron Celestian,Natural History Museum of Los Angeles County
The Victorian Orchid, a Fancy Vivid Purple, appears more pink or more purple depending on your perspective.
Courtesy Brian Lazar
The Rainbow Necklace features differently colored stones, including extremely rare blue-gray diamonds.
Christies Images Ltd 2016
The Oppenheimer Blue, the world's largest blue diamond, sold for $57.5 million at Christie's Geneva on May 18, 2016, making it the most expensive diamond ever sold at auction.
Christies Images Ltd 2016
The 14.62 carat Fancy Vivid stone is mounted on a platinum ring and flanked on either side by a trapeze-shaped diamond.
courtesy sotheby's
The Unique Pink is the largest Fancy Vivid pink pear-shaped diamond ever to be offered at auction.
courtesy sotheby's
The diamond was sold for $31.6 million by Sotheby's at an auction in Geneva in May 2016. The price makes it the most expensive Fancy Vivid pink diamond to sell at auction.
courtesy sothebys
A rare Fancy Vivid Blue diamond ring valued at $25 million will go up for auction on November 16, 2016. The diamond is known as the Sky Blue diamond.
courtesy christies
The Aurora Green is the largest Fancy Vivid green diamond ever sold at auction. The stone went under the hammer on May 31, 2016 at Christie's auction house in Hong Kong, selling for $16.8 million.
Sotheby's
Sotheby's auctioned this 9.54 carat ring it says belonged to child star Shirley Temple on April 19, 2016. Though it was expected to fetch between $25 million and $35 million, it failed to sell.
CNN
In April 2016, the De Beers Millennium Jewel 4 broke auction records in Asia.
courtesy sotheby's
The stone sold for $31.8 million, making it the most expensive piece of jewelry sold at an auction in Asia.
CNN  — 

As the head of jewelry in Asia for British auction house Bonhams, Graeme Thompson is used to handling beautiful diamonds on a daily basis. Yet he’s only ever held a red diamond once, about five years ago. “Red diamonds are the rarest of them all and whoever gets to hold one in his hand is very lucky indeed,” he said.

Mining company Rio Tinto has been showcasing stones from its Argyle mine in Western Australia for the past 33 years – and during that time, less than 20 carats of Fancy Red certified diamonds have been sold.

Fancy Red diamonds are on the pink diamond color spectrum and is a grading from the Gemological Institute of America.

On Wednesday in New York, Rio Tinto unveiled its largest Fancy Red diamond yet to a select group of collectors, alongside other gemstones in its annual tender of pink diamonds. Known as the Argyle Everglow, the polished radiant cut diamond weighs 2.11 carats.

It represents “rarity within rarity, and will drive global demand from collectors and connoisseurs in search of the incomparable,” said Argyle Pink Diamonds Manager Josephine Johnson.

The stone is “half the size of a one cent coin, but I expect it to sell for over $10 million,” said Tobias Kormind, Managing Director of 77Diamonds.com, Europe’s largest online diamond jeweler.

Thompson said he was not comfortable making a more definitive prediction on price without having seen the stone, but that the determining factors will be “the carat weight, the strength of the color, how red it is, and the clarity. The difference in value between a stone that is very clean and one that has inclusions is huge.”

Fetching high prices

The largest red diamond in the world, the 5.11 carat Moussaieff Red, was discovered in Brazil in the 1990s and is currently owned by jeweler Moussaieff.

Significant red diamonds rarely appear at auctions. In 2013, a 1.92-carat Fancy Red rectangular-cut diamond, sold for CHF3.15 million at Christie’s, while the auction house also sold a 2.09-carat heart-shaped Fancy Red diamond ring by Moussaieff for HKD39.32 million in 2014.

Argyle diamonds
The 2.42 carat Fancy Purple-Pink Argyle Avaline and the 1.14 carat Fancy Red Argyle Isla.

“The color red is essentially a highly, highly saturated vivid pink, where the body color goes beyond the pink color range – and there can be modifying color to that red, like pinkish red, orangey red, brownish red – and all of these contributing factors will then determine the value of the diamond,” Thompson explained. “A Fancy Red is the rarest of all diamonds.”

“To hold a red diamond in your hand and look at it and say it’s a truly a red stone without any modifying colors, very few people on this planet will ever be able to do that,” Thompson added, noting such red diamond will appeal to Chinese buyers “as it is the most auspicious of colors in China.”

Mine to close soon

The Argyle Diamond Mine produces 90% of the world’s rare pink diamonds and is set to close by 2021, according to Robyn Ellison, communications manager for Rio Tinto.

“It is unlikely that a diamond as rare as this will come out of the mine again,” Ellison said.

At Rio Tinto’s annual tender this year, buyers will have a choice of 58 diamonds weighing a total of 49.39 carats. They include five “hero” diamonds selected for their unique beauty and named to ensure there is a permanent record of their contribution to the history of the world’s most important diamonds.

The collection will be showcased in Hong Kong and Perth with bids closing on October 11.

CNN’s Zahra Jamshed contributed to this report.