(IDEX Online) - Petra is to sell a unique collection of blue diamonds, recovered within a week at its iconic Cullinan mine, in South Africa.The Type IIb diamonds, weighing between 9.61 carats and 25.75 carats, are all described as being of significant color, clarity, size. They contain a small amount of boron, which determines their blue color.They've been named Letlapa Tala, which means "blue rock" in Pedi, the predominant language spoken locally.Petra Diamonds Limited agreed a restructuring deal earlier this week with South African lenders in the face of $650m of debts.It says the Letlapa Tala collection (pictured) is probably first time five blue rough diamonds have ever been offered for sale at one time.Buyers can bid for any or all of the stones. Viewings will take place in Antwerp, Hong Kong and New York, and the tender will close on 24 November.