Welcome to the third chapter of Captivated by Colour and this time, blue diamonds are in the spotlight. Considered one of the rarest colours, blue diamonds have an enigma and appeal that very few other colours hold. It’s still April, so diamonds are still the birthstone for the rest of the month. It’s only a small and exclusive group of people around the world who will ever own a blue diamond, but in case you’re thinking of investing in one (because blue diamonds are investment diamonds), here’s all you need to know.

What gives blue diamonds their colour?

Like yellow diamonds, blue diamonds are a result of chemical imperfections in the crystal lattice. When the element boron (B on the periodic table) replaces a carbon atom in the diamond structure, it will impart a blue colour to the diamond. The more boron impurities in the diamond, the deeper the resulting blue colour.

Where do blue diamonds come from?

Once again, South Africa can lay claim to fame here. The Cullinan Diamond Mine, located just outside of Pretoria, South Africa, is the world’s most important source of blue diamonds. Once owned by diamond giant De Beers, it was purchased by Petra Diamonds in November 2007, who have since recovered many significant and important large, blue diamonds. Other countries in which blue diamonds have been found include India, Australia and Botswana.

Cullinan Diamond Mine South Africa

Cullinan Diamond Mine, located north of Pretoria, South Africa is the source of not only the world’s biggest diamond ever, but also most of the world’s blue diamonds. Image: Petra Diamonds.

Scientific studies have recently shown that blue diamonds grew in some of the most extreme geological conditions known. A paper published by respected science journal Nature in August 2018 revealed that blue diamonds originate from depths approximately four times deeper than most diamonds. The study of inclusions in rare blue diamonds showed that originate at depths of 660km, or more, below the surface of the earth, in the presence of subducted oceanic plates.

How are blue diamonds graded?

As we mentioned in our previous articles on yellow diamonds and pink diamonds, the colour of blue diamonds is graded according to the hue, tone and saturation. Many blue diamonds have undertones of grey and these diamonds are considered less desirable (and therefore less expensive) than the Fancy Vivid or Fancy Intense colours. The clarity of blue diamonds is graded in an identical fashion to white diamonds, with Flawless and Internally Flawless diamonds being the most valuable, moving down to Included diamonds.

GIA blue diamond scale

Blue diamond colour grading chart, as defined by the GIA. Image: GIA

How much is a blue diamond?

Blue diamonds are, without a doubt, some of the most expensive diamonds in the world. The Blue Moon of Josephine diamond, a 12.03ct cushion cut diamond sold for just over $4million per carat, the highest per carat price ever paid for a diamond on auction.

If we look at some smaller sized blue diamonds, we’ve seen a 0.12ct marquise cut fancy greyish blue diamond at $4800 (~ R89,280) and a 0.15ct fancy intense blue square cut for $10,500 (~ R195,300). Despite South Africa being the source of many blue diamonds, there are very few available for sale in the country at the moment.

What are some famous blue diamonds?

The Hope Diamond

Perhaps the most famous of the blue diamonds, the Hope Diamond has a chequered and intriguing history. Discovered in India, and weighing approximately 112.5ct as a rough diamond, it’s earliest history can be traced back to French gem merchant Jean-Baptiste Tavernier who acquired the diamond in the mid 17th-century. After passing through the hands of multiple royals, it was purchased in 1911 by American socialite Evalyn Walsh McLean. After her death in 1947, it was purchased by Harry Winston before he donated it to the Smithsonian Institute in 1958. The Hope Diamond has been described by the GIA as Fancy Dark Greyish Blue, weighing 45.52ct.

Hope diamond blue diamond

The infamous blue Hope Diamond, pictured out of it’s setting at the Smithsonian Institute. Image: Wikipedia Commons.

The Blue Moon of Josephine

If you’ve read our article on pink diamonds, you may be thinking that the name “Josephine” sounds familiar. That’s because the Blue Moon diamond (as it was previously known) was purchased by Joseph Lau, the same buyer of the “Sweet Josephine” pink diamond! The Blue Moon diamond is a South African diamond, discovered at the Cullinan Diamond Mine in January 2015. Weighing a significant 29.6ct in size, it was sold to Cora International for $25.5 million dollars. Over the course of 6 months, Cora Intl. cut and polished a 12.03ct cushion cut diamond of flawless clarity and Fancy Vivid Blue colour. How much did Mr Lau pay for the Blue Moon? A cool $48.5 million (over $4 million per carat), a world record price per carat for any diamond, ever.

Blue Moon South African blue diamond

On the left, the 29.6ct rough diamond found at Cullinan Diamond Mine. On the right, the cut and polished Blue Moon of Josephine diamond, weighing 12.03ct. Image: Petra Diamonds.

The Oppenheimer Blue

The Oppenheimer name is synonymous with diamonds. Four generations of Oppenheimer sons (Ernest, Harry, Nicky & Jonathon) have been chairman of global diamond giant De Beers, and it makes sense that one of the world’s most valuable diamonds carries the Oppenheimer name. Formerly owned by Phillip Oppenheimer, the nephew of Sir Ernest Oppenheimer, the 14.60ct emerald cut blue diamond was auctioned by Sotheby’s in 2016. When the hammer fell at $57.5 million, it was, at that stage the highest price ever paid for a diamond on auction (that record later fell to the Pink Star diamond). The Oppenheimer Blue is the largest Fancy Vivid blue diamond (as classified by the GIA) ever auctioned. Whilst the exact mine that gave rise to the Oppenheimer Blue diamond is unknown, it is certain that the diamond is South African in origin.

Oppenheimer Blue Diamond from South Africa

The magnificent 16ct Oppenheimer blue diamond, set in a ring. Image: Sotheby’s.

With that, we’re wrapping up our article on blue diamonds. Now you know how critical South Africa has been in supplying many of the world’s blue diamond treasures, we hope you’ll appreciate our diamond heritage even more. If you are shopping for fancy colour diamonds in South Africa, why not contact us to see what we have available and we can discuss your exact loose diamond requirements. We’ll be able to offer you wholesale prices that are far cheaper than you’d find at retail jewellery stores in Sandton City, Hyde Park, Rosebank or the Cape Town Waterfront.