Petra Diamonds has sold a 39.19ct blue diamond for $8.8m (£5.5m). This sale is the latest in a spate of large-diamond sales, reflecting a trend in the market for investment in large diamonds, despite the global financial turmoil. 

The diamond, which was discovered at the Cullinan mine in South Africa, was put on tender in Johannesburg, South Africa last month.

Petra Diamonds chief executive officer Johan Dippenaar said: “Blue is one of the most rare colours of diamond and this exceptional stone is even more special due to its unusually large size. Diamonds of this nature are true collectors’ items due to their incredible beauty and scarcity.”

While the sale of the diamond was made through a third party and no confirmation has been made, it is thought that the diamond was bought by London jeweller Moussaieff.

The large-diamond market has been enjoying success in the downturn. Christie’s auction house in New York reported strong diamond sales in line or higher than pre-sales estimates during its October 15 auction. Buyers at the sale included Dubai diamonds dealer Amer Radwan and Moussaieff.

Christie’s head of jewellery Rahul Kadakia said: “In a volatile market when the Dow lost 700 points in a day, nearly $30m of jewellery and precious stones changed hands at Christie's in less than five hours, thus demonstrating the relative stability of the jewellery market and the long dependability of gems as a store of portable value."

Despite these buoyant results for large diamonds, smaller diamonds have been struggling in the downturn. De Beers has reduced the number of diamonds it will sell in the remainder of this year to tackle softening diamond prices.

De Beers outlined its intentions in a letter to sightholders, which are companies on the De Beers-controlled Diamond Trading Company’s (DTC) list of authorised bulk purchasers of rough diamonds. DTC sales and client service director Mahiar Borhanjoo wrote: “We recognise that consumers will buy fewer, better things and this will create real opportunities for diamonds. To ensure our commitment is heard, we are expecting to have two smaller sights for the remainder of the year.”