Petra, which anticipates that the diamond will be sold via a special tender, said that biddings via its online platform will close on July 12.
While it didn’t set a price range for the stone, the miner said high-quality blue diamonds like the one for sale usually fetch the highest values.
Petra’s Blue Moon of Josephine diamond, cut from a 29 carat rough blue diamond, sold for $48.5 million in 2015.
The figure corresponds to a price of $4 million per carat, which remains the world record price per carat ever paid for a diamond.
Cullinan is known as the world’s most important source of blue diamonds, as well as being the birthplace of the 3,106-carat Cullinan diamond, which was cut to form the 530-carat Great Star of Africa. The operation also yielded the 317-carat Second Star of Africa. They are the two largest diamonds in the British Crown Jewels.