Another rare blue diamond found

A replica Cullinan Diamond, with the nine stones it was cut into.

"They are so rare that there aren't official statistics on their discovery rate," says Cathy Malins, Petra's corporate communications manager. In the five years that Petra has operated the mine, over 15-million tons of rock have been brought to the surface, producing about 5-million carats but only three world-class blue diamonds, she adds.

A carat refers to the weight of a diamond. One carat weighs 0.2 grams. The diamonds are recovered from one of the biggest kimberlite pipes in the world. Kimberlite is named after the South African diamond mining town of Kimberley, where the gems were first discovered in the country. It refers to a type of potassic volcanic rock known to contain diamonds.

Cullinan is some 40km northeast of Pretoria in Gauteng Province. The mine goes to a depth of 732 metres, where this blue diamond was found. "Once the ore is transported to surface, it goes through the processing plant and the blue diamond was recovered during the normal process of concentrating underground material, with final recovery by method of x-ray," says Malins.

In the past five years, several blue diamonds have been recovered at Petra, including a 26.6 carat rough stone which was cut into a flawless and vivid blue 7 carat stone that sold for US$9.49-million - or US$1.35-million per carat - on auction in May 2009. At the time, it was the highest price per carat for any gemstone sold on auction, and the highest price for a blue diamond sold on auction. It was named the Star of Josephine by its new owner, a Hong Kong property tycoon.

Malins indicates that it is not clear exactly at present what will be done with the latest discovery. "The blue is currently being evaluated in order to decide the best route to market," she says.

In all, the Cullinan Mine has yielded 11 rare blues which were displayed in 2000 at London's Millennium Dome alongside the Millennium Star. Famous larger blues recovered at the mine include the 27 carat vivid blue Heart of Eternity, and an unnamed 39.2 carat rough blue which was recovered and sold in 2008.

Petra Diamonds indicates that demand for the gems continues to rise, particularly in developing countries like China and India. "Demand growth for diamonds in emerging markets is expected to continue as global wealth and consumer spending increase," says the mining house.

At present, there are 30 significant diamond mines operating in the world today. "To date, the most important discoveries (other than Argyle in Australia) have clustered into three regions of the world: southern Africa, Siberia, and western Canada."

The Cullinan Diamond

The world's most famous diamond was found in Cullinan around 1905 by Frederick Wells. Thomas Cullinan had bought the farm Elandsfontein in 1903 when he heard that an English prospector, Perceval Tracey, had found a three carat diamond on the neighbouring farm. The diamond was found nine metres down, protruding from the pit wall.

Known as the Cullinan Diamond, it was 3 106 carats and measured 10.5cm across, and was as large as a man's fist. The huge diamond was cut into nine diamonds of varying sizes, the largest, named Cullinan 1 or The Great Star of Africa, weighed 530.2 carats. It is the second largest polished diamond in the world. It, together with the lesser Star of Africa or Cullinan II, forms part of the British Imperial State Crown, and are on display in the Tower of London. They were given to King Edward VII of England on his 66th birthday.

The largest polished diamond in the world, the 545 carat Golden Jubilee, also comes from Cullinan. Thomas Cullinan, who was later knighted, was a building contractor. His house, on the ridge in Parktown, Johannesburg, still exists. He remained involved in the mine until 1923, when he resigned as chairman. He died in 1936.

Other large diamonds

Other large diamonds recovered at Cullinan include the Premier Rose (353 carats), the Niarchos (426 carats), the De Beers Centenary (599 carats), the Golden Jubilee (755 carats) and the famous Taylor-Burton diamond (69 carats). More recently, the Cullinan Heritage, with 507 carats, was recovered and sold for US$35.3-million in 2010, the highest price ever obtained for a rough diamond.

Over the years, the mine has produced more than 750 stones weighing more than 100 carats, 130 stones weighing more than 200 carats, and around a quarter of all diamonds weighing more than 400 carats. Prospects for its future are good - it has been estimated that the lifespan of the mine could still be more than 50 years.

Petra acquired the Cullinan Mine in 2008, and has interests in eight other mines, seven of which are in South Africa; one is in Tanzania. It also has an exploration programme in Botswana.

When the mine was first established, about 26 000 workers were employed in the operation. Nowadays, just 1 200 people work the mine, going down 760 metres by means of 560 kilometres of tunnels. The early excavations have left a large hole, which is three times bigger than the more famous Kimberley hole in the Northern Cape. The vast hole measures a kilometre across and half-a-kilometre wide, and leaves a gap going down into the earth of 700 metres. It is continually widening, as 80 000 tons of rock fall into it every year.

Original village

The original village of Cullinan is largely intact, with a row of semi-detached stone Edwardian houses on either side of Oak Street, now converted into curio and craft shops, interspersed with coffee shops and restaurants. Larger houses within the mine property, with their green roofs and white fascias, belonged to mine managers. A Masonic Hall, a number of churches and a recreation hall, all dating back to the early 1900s and built in local sandstone, indicate the diversity of the early mining community. These days the village consists of 460 houses.

The McHardy House Museum in Oak Street belonged to William and Evalina McHardy and their seven children. McHardy was the general manager of the mine and the house was built in 1903. After the deaths of the two daughters in 1984, the mine bought the contents of the house and turned it into a museum. The museum, like many other shops and restaurants in the village, is open every day except Tuesdays.

A steam train leaves from Pretoria on the weekends, taking commuters for a day trip to the village and back again. Several tour companies offer tours of the mine and village, providing an informative look inside the operation of hauling large skips above ground, taking the rock to be crushed and washed, and once fine sorting has taken place, to be hauled off to join a mountain of discarded rock being created west of the site.

Visitors walk near the big hole. Jacaranda, pepper and coral trees that dot the site, are reminders of another time. The tour ends in the mine shop, where diamonds ranging from R23 000 to R2.3-million can be bought. Diamond cutting can also be observed.

On display is a 66-faceted diamond, referred to proudly as the Cullinan cut, a cut that is unique to the Cullinan Mine. A glance at the diamond through a magnifying glass reveals a beautifully crafted gemstone.