It is well known that Diamond is the hardest stone on earth, due to the close packing of the carbon atoms and the regularity in the crystal structure (for more on this read my post on Diamonds). These same qualities gave it unique optical and physical properties: remarkable transparency, an adamantine lustre, strong refraction (brilliance) and dispersion of the light (fire) all the things that make a diamond so particular and magical. Consequently, when most people think about diamonds, the majority will have in mind a beautiful, crisp white transparent gemstone with a strong lustre and brilliance. That said, although most of these gems are colourless or white ( the term is known by most people), one in 10,000 diamonds will be coloured.
Due to different reasons that I will explain below, diamonds come in a range of colours:
- brown (the most common)
- red (the rarest)
The paucity of the supply of gem-quality coloured diamonds and the increased interest and demand for them makes them incredibly valuable.
What are ‘fancy diamonds’ and what gives them colour?
Often, what give a diamond a particular colour are the changes to its atomic structure.
Let’s start with the most common ones: yellow and brown.
A hint of yellow in a diamond is due to the presence of nitrogen atoms, either as single atoms or as groups of aggregates. If the diamond has individual particles, it’s known as a type Ib, commonly called a Canary diamond due to its famous Canary yellow colour. Although originally this term was just used for this type of diamond, nowadays it is utilised for all fancy yellows. When the presence of nitrogen atoms is in groups, then the diamond is a type Ia. The presence of a yellow tinge is evident in diamond graded H to Z and all the intense tinted yellows.
The cause of colour in brown diamonds (the most common diamond colour in nature and the earliest found in Roman rings) is due to a phenomenon called “plastic deformation”, where the crystal structure is affected, and the regularity of the lattice is disturbed. Most large brown diamonds originate from South Africa, but a number also come from the Argyle mine in Australia. Realising how valuable and trendy coloured diamonds have become, jewellers have begun marketing these gemstone as “champagne ”or “cognac” – even “chocolate”. Plastic deformation is also the primary cause for the formation of pink and red diamonds.
Blue diamonds are as desirable as they are rare. The main cause of colour in this type of fancy diamond is the presence of the chemical element Boron. One atom of boron per 1 million atoms of carbon can have a significant influence and will determine the colour of this precious gemstone.
A rare colour of all fancy coloured diamonds is the green diamond. A green colour in diamond occurs when a diamond’s crystal structure is damaged by millions of years of exposure to a radioactive source. Irradiation is common in diamond crystals found in alluvial deposits in Brazil, India and Central Africa, reflecting the greater amount of uranium compounds existent in sedimentary rocks found in these locations. he best example of a green diamond is the famous 40.70-carat Dresden Green. This beautiful diamond derives its name from the capital of Saxony where it has been on display for more than two hundred years. The earliest known reference to its existence occurs in the Post Boy, a London newssheet of 25-27 October 1722. It is believed to be from India or Brazil.
What are the prices for fancy diamonds?
Only recently, Sotheby’s and Christies both sold two beautiful coloured diamonds in Geneva for astronomical prices:
The Blue Moon of Josephine
On November 2015, Sotheby’s sold a 12.03 carat blue cushion-cut diamond at auction for a record-setting price of $48.4 million. GIA rated it as a flawless, fancy vivid diamond, and it set the world record for the highest price per carat ever paid for a coloured gemstone.
The Sweet Josephine
On the previous day to the Sotheby’s auction, Christie’s sold a 16.08 carat pink diamond for $28.5 million, also a record price that exceeded the estimate of $23-28 million. This fancy vivid pink diamond, owned by an American family for 15 years, is the largest cushion-cut ever sold and is one of only three fancy pink Diamonds over ten carats that has been sold in the last 250 years.
A businessman from Hong Kong bought both of these fancy diamonds for his eight-year-old daughter, Josephine. Lucky girl!
Other famous coloured diamonds include:
The 0.95 carat purple-red that Christies auctioned in 1987 for $1 million dollars in New York. It is believed to have originated from Brazil.The 45.52 carat Hope Diamond, a beautiful blue diamond discovered in India.The Wittelsbach diamond, a dark-blue 35.50-carat, which, after a few royal owners, landed in the hands of the famous jeweller Laurence Graff.The Blue Heart, a rare 30.62-carat heart-shaped blue diamond that was donated by its last owner Marjorie Merriweather to the Smithsonian Institution in Washington where it remains on display today. She previously bought this stunning piece from Harry Winston who had it mounted in a ring.
*all images are from pinterest.com