A rare 39.34 carat Type IIb blue diamond recovered at Petra Diamonds' Cullinan mine is set to go on auction in July.

Petra said the famed Cullinan Diamond Mine, located at the foothills of the Magaliesberg mountain range, 37km northeast of Pretoria, is renowned as a source of large, high-quality gem diamonds, including Type II stones, as well as being the world’s most important source of very rare blue diamonds.

Petra said the unique geology of the Cullinan kimberlite pipe means that the majority of its diamonds are aged between 3.2 and 1.1 billion years old — spanning a time in the Earth’s history from before the formation of the first major continents to the beginnings of multicellular life.

However, Petra said Type IIb blue diamonds are so rare that their age has not been established.

The company said the Cullinan mine earned its place in history with the discovery of the Cullinan diamond in 1905, the largest rough gem diamond ever found, at 3,106 carats. It said many of the most famous diamonds in the world come from the Cullinan mine.

Notable diamonds historically produced from the Cullinan Mine include the Premier Rose (353 carats rough); the Niarchos (426 carats rough); the De Beers Centenary (599 carats rough); the Golden Jubilee (755 carats rough); and the Taylor-Burton diamond (69 carats polished).

More recently, remarkable diamonds recovered by Petra at the mine include:

• the Cullinan Heritage (507 carats rough white diamond), which sold for $35.3m in 2010;
• the Blue Moon of Josephine (29 carats rough blue diamond), which sold for $25.6m in 2014;
• the Cullinan Dream (122 carats rough blue diamond), which sold for $25.3m in 2016;
• the Legacy of the Cullinan Diamond Mine (424 carats rough white diamond), which sold for just under $15m in May 2019;
• the Letlapa Tala Collection (a collection of five blue diamonds of high quality and clarity) which sold for $40.36m in November 2020; and
• the carat Type IIa white gem quality diamond which sold for $12.18m in March 2021.

Petra Diamonds said viewings of the Type IIb blue diamond would take place in Antwerp, Belgium, between June 15 and 18, Dubai on June 22 and 23, Hong Kong on June 29 and 30, and New York on July 7 to 9.

The company said the tender on Petra’s online bidding platform is planned to close on July 12.

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