The Argyle Diamond Mine is a diamond mine located in the East Kimberley region in the remote north of Western Australia. Argyle is the largest diamond producer in the world by volume, although due to the low proportion of gem-quality diamonds, is not the leader by value. It is the only known significant source of pink diamonds, producing over 90% of the world's supply. It additionally provides a large proportion of other naturally coloured diamonds, including champagne, cognac and rare blue diamonds. Argyle is currently transitioning from an open pit mine to an underground mine.
The Argyle diamond mine is also notable for being the first successful commercial diamond mine exploiting a volcanic pipe of lamproite, rather than the more usual kimberlite pipe; much earlier attempts to mine diamonds from a lamproite pipe in Arkansas, USA were commercially unsuccessful. The Argyle mine is owned by the Rio Tinto Group, a diversified mining company which also owns the Diavik Diamond Mine in Canada and the Murowa Diamond Mine in Zimbabwe.
A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or colour. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The colour of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's colouration, a diamond's colour can either detract from or enhance its value. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable. Out of all coloured diamonds, red diamonds are the rarest. The Aurora Pyramid of Hope displays a spectacular array of naturally coloured diamonds, including red diamonds.The legend of Argyle pink diamond has grown over the past ten years. At the 1989 Christie's auction in New York a 3.14 carat Argyle pink sold for $1,510,000. Privately, Argyle has sold pink diamonds for up to $1 million a carat. For years the white diamond was considered the world's most beautiful diamond, until the discovery of the Argyle mine heralded the arrival of the Argyle pink diamond. Never before had pink diamonds displaying such intense shades of colour been seen. The pink diamonds of India, Brazil and Africa were characteristically light in colour and paled even further when placed beside the intensely pink Argyle diamonds. The natural colour diamonds have in fact been around as long as the classical whites but in much smaller quantities and never in great demand. The Argyle pink diamond comes in shades ranging from delicate pastel rose to robust raspberry and full-blooded purple-reds. The prices per carat are determined by the intensity of colour. Argyle selects only its most vibrant pink diamonds for polishing at its head office in Perth. There, the stones are polished in a wide range of cuts, such as round brilliant, marquise, oval and pear, to enhance their natural beauty. Polished pink diamonds are available in the same size ranges as traditional commercial sizes. Once a year, Argyle Diamonds issues a special release of outstanding pink diamonds that are sold by special bids in the international and invitation-only, Pink Diamond Tender.
Grading White Diamonds
The majority of diamonds that are mined are in a range of pale yellow or brown colour that is termed the normal colour range. Diamonds that are of intense yellow or brown, or any other colour are called fancy colour diamonds. Diamonds that are of the very highest purity are totally colourless, and appear a bright white. The degree to which diamonds exhibit body colour is one of the four value factors by which diamonds are assessed.
History of Colour Grading
Colour grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate.
As the diamond trade developed, early diamond grades were introduced by various parties in the diamond trade. Without any co-operative development these early grading systems lacked standard nomenclature, and consistency. Some early grading scales were; I, II, III; A, AA, AAA; A, B, C. Numerous terms developed to describe diamonds of particular colours: golconda, river, jagers, cape, blue white, fine white, and gem blue, "brown".
Grading The Normal Colour Range
Refers to a grading scale for diamonds in the normal colour range used by internationally recognised laboratories (GIA & IGI for example). The scale ranges from D which is totally colourless to Z which is a pale yellow or brown colour. Brown diamonds darker than K colour are usually described using their letter grade, and a descriptive phrase, for example M Faint Brown. Diamonds with more depth of colour than Z colour fall into the fancy colour diamond range.
Diamond colour is graded by comparing a sample stone to a masterstone set of diamonds. Each masterstone is known to exhibit the very least amount of body colour that a diamond in that colour grade may exhibit. When sample stones are compared with the master stone, the grader assesses whether the sample has more, less or equal colour to the masterstones. A grading laboratory will possess a complete set of masterstones representing every colour grade. However, the independent grader working in a retail will possess a range of masterstones that covers only the typical grade range of color they expect to encounter while grading. A typical grading set of masterstones would consist of five diamonds in two grade increments, such as an E, G, I, K, and M. It is not common for a grader to possess a D masterstone, as the E masterstone is more useful in dividing the D and E colour grades. The intermediate grades are assessed by the graders judgement.
Diamonds in the normal colour range are graded loose, with the table facet facing downward and pavilion side upwards. When colour grading is done in the mounting, other techniques will apply and the grade will usually be expressed as a range (for example F-G)
Grading Fancy Colour Diamonds
Yellow or brown colour diamonds having colour more intense than "Z", as well as diamonds exhibiting colour other than yellow or brown are considered fancy coloured diamonds. These diamonds are graded using separate systems which indicate the characteristics of the colour, and not just its presence. These colour grading systems are more similar to those used for other coloured gemstones, such as ruby, sapphire, or emerald, than they are to the system used for white diamonds.
Coloured Diamond Grading System
It refers to the colour grading system used by internationally recognised laboratories (GIA and IGI for example) for colours that are not in the normal colour range of diamonds. These laboratories use a list of 27 colour hues that span the full spectrum of colours. The tone and saturation of these hues are then described with one of nine descriptors:
- Very Light
- Fancy Light
- Fancy Dark
- Fancy Intense
- Fancy Deep
- Fancy Vivid
The grading has an additional aspect that describes how well is the color applicable on the diamond.
Color can also be determined using a device called the Gran Colorimeter, manufactured by Sarin Technologies. It measures from D to Z to Fancy Intense with an accuracy within +/-½ of a colour grade on loose stones from 0.25 to 10 carats (50 to 2,000 mg) (as low as 0.15 carat (30 mg) or as high as 20 carats (4 g) with reduced accuracy). The colorimeter provides output in various grading scales including GIA, GEM, IGI, AGS, and HRD. The accuracy is within +/-1 color grade for mounted stones.
The Gran colorimeter was first developed by Paul Gran in 1972 at Gran Computer Industries Ltd.
Value of Coloured Diamonds
The Darya-I-Nur Diamond is one of the world's largest diamonds and is one of the rarest because of its pale pink colour. It weighs about 182 carats (36.4 g). Its exact weight is unknown because it has been mounted in its brooch setting for over 130 years. Its Persian name 'Darya-I-Nur' translates into English as the 'River of Light'.
Diamonds that enter the Gemological Institute of America's scale are valued according to their clarity and colour. For example, a "D" or "E" rated diamond (both grades are considered colourless) is much more valuable than an "R" or "Y" rated diamond (light yellow or brown). This is due to two effects: high-colour diamonds are rarer, limiting supply; and the bright white appearance of high-colour diamonds is more desired by consumers, increasing demand. Poor colour is usually not enough to eliminate the use of diamond as a gemstone: If other gemological characteristics of a stone are good, a low-colour diamond can remain more valuable as a gem diamond than an industrial-use diamond, and can see use in diamond jewellery.
Diamonds that go out of scale in the rating are known as "fancy colour" diamonds. Any light shade of diamond other than light yellow or light brown automatically falls out of the scale. For instance, a pale blue diamond won't get a "G" or "K" colour grade, it will get a Faint Blue or Light Blue grade. These diamonds are valued using different criteria than those used for regular diamonds. When the colour is rare, the more intensely coloured a diamond is, the more valuable it becomes. Another factor that affect the value of Fancy-Coloured diamonds is fashion trends, so pink diamonds fetched higher prices after celebrity Jennifer Lopez was photographed wearing a square-shaped pink diamond.
Fancy-coloured diamonds such as the deep blue Hope Diamond are among the most valuable and sought-after diamonds in the world. In 2009 a 7 carat blue diamond fetched the highest price per carat ever paid for a diamond when it was sold at auction for 10.5 million Swiss francs (US$9.5 million at the time) which is in excess of US$1.3 million per carat.
The Aurora Pyramid of Hope's collection of natural coloured diamonds is one of the most comprehensive diamond collections in the world.