Petra Diamonds plans to hold a special tender of five blue diamonds it recovered from the Cullinan mine in South Africa last month.

The sale of the Letlapa Tala collection, which means “blue rock” in the northern Sotho language spoken in the region, marks the first time this number of blue diamonds has been offered for sale at once. The high-quality, type IIb stones range from 9.61 to 25.75 carats, and were all found in one week, the miner noted.

The Letlapa Tala collection could fetch between $30 million and $40 million, according to Liberum analyst Ben Davis, while Berenberg has valued it at $26 million, or $300,000 per carat.

The last significant blue diamond Petra sold was a 20.08-carat, type IIb, which it discovered last year. That stone went for $14.9 million, or $741,000 per carat.

Petra will preview the stones in Antwerp, Hong Kong and New York prior to the November 24 tender.