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pink diamond

Photo courtesy of Sotheby’s.



One of only two internally flawless fancy vivid pink diamonds of over 10 carats ever to come to auction, The Williamson Pink Star, is expected to make waves when offered at Sotheby’s in Hong Kong on October 5, and has being forecast that it will sell for more than $21 million. The exceptional gemstone also is a testament to the Williamson Mine, located in Tanzania, which more than 80 years became the first well known African diamond mine to begin operating outside of South Africa.

The Williamson Pink Star, which will be offered in a standalone, single-lot auction, is currently on a world tour to promote the sale, visiting Dubai, Singapore and Taipei, before returning to Hong Kong.

The stone is outsized only by the record-breaking CTF Pink Star, the 59.60-carat oval mixed-cut diamond, which sold at Sotheby’s for $71.2 million in April 2017, and still holds the world auction record for any diamond, gemstone or jewel. Like the CTF Pink Star, the Williamson Pink Star was also polished by Diacore, a South African manufacturer specializing in massive cuts. The first earlier achieved fame by cutting and polishing the 203.04-carat De Beers Millennium Star.


“The discovery of a gem-quality pink diamond of any size is an extremely rare occurrence – something that, with the recent closure of the Argyle mine, seemed until recently highly improbable. Driven by a limited supply and rising demand, prices for top-quality large pink diamonds over 5 carats have increased exponentially over the past decade, serendipitously setting the scene for the appearance now of this one-of-a-kind stone,” said Wenhao Yu, Chairman of Jewellery and Watches at Sotheby’s Asia.

Pink remain one of the rarest colours to occur naturally in diamonds. Of all the diamonds submitted to GIA, fewer than 3 percent are classified as colored diamonds, and, of those, less than 5 percent of those are considered predominantly pink. An even smaller proportion have a hue strong enough colour to classify them as “fancy vivid pink,” and most of those are relatively small in size.

pink diamond

The 11.5-carat vid pink Williamson Pink, which will go on sale at Sotheby’s on October 5, 2022. 

A fancy vivid pink diamond, weighing more 10 carats is therefore of the utmost rarity . The two most famous to date are the already mentioned CTF Pink Star, and the “Williamson,”

The latter, which is different stone to the Williamson Pink Star, is a brilliant-cut diamond of 23.60-carats that gifted as a wedding present to the then Princess Elizabeth II in 1947, when she married Price Phillip, by the Canadian geologist and royalist, Dr. John Thorburn Williamson. It was he who owned the namesake Williamson mine in Mwadui, Tanzania, which also is where the Williamson Pink Star was also discovered.

The Williamson was cut from a 54.5-carat rough diamond and set as the centerpiece of a brooch designed by Cartier. It is said to be one the queen’s favorite jewelry pieces.

The open-pit Williamson Mine in Tanzania. Photo credit: Wikipedia Commons.


The Williamson Diamond Mine, which is also known as the Mwadui mine, is located 23 kilometers northeast of Shinyanga in Tanzania. Established in 1940, over its lifetime it has produced more than 19 million carats of rough diamonds.

Originally owned by John Thorburn Dr. Williamson, the mine was later nationalized by the government of Tanzania, and in February 2009 became controlled by Petra Diamonds, with 75 percent ownership. the government of Tanzania continued to own the remaining 25 percent.

The mine was predominantly an open pit operation, with the large pit reaching a depth of about 90 meters.

Its most important geological feature is the kimberlite pipe on which it is located. At 146 hectares in area at surface level, it ranks as the largest economically exploitable diamond-bearing volcanic pipe in the world.

Drill cores conducted by De Beers in the 1990s indicated that it may be possible to extend the current 90-meter deep open pit to as much as 350 meters deep, and continue down even further with underground mining operations.

But at present, however, the mine is largely dormant. In April 2020, it was was mothballed by Petra after the collapse of diamond prices. And, athough in February 2021 Petra and the Tanzanian Government entered discussions to reopen the mine in the fourth quarter of last year, that did not come to pass.

In September 2021 Petra announced that it was seeking a buyer for the Williamson mine.