The gemstone laboratories | Unsaid Library

The gemstone laboratories

Gemstone laboratories are exclusively concerned with the evaluation of polished gemstones. The four “C’s” described above are assessed using the most modern means and techniques. The end result is laid down in the certificate on which the details of the four assessments are stated with as extra assessment the “Finish Grade”, which plays an extra role in larger and higher qualities. The certificate has a number that refers to the worksheet on which the stone is identified and graduated. This number is placed in the circle with a laser. A microphoto is made of the certificate. This microphoto is “sealed” at the same time as the stone.

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Certified stones are also often used as part of an investment portfolio and disappear into a safe to be re-traded at a later date. If the stone is removed from the seal to be used in jewellery, the stone can be identified at a later date on the basis of the number and worktop and then re-sealed.

Some examples of laboratories are: Hoge Raad voor de Diamant (HRD), Dutch Gemstone Laboratory, International Gemological Institute (IGI), Gemological Institute of America (GIA). In 2012, the High Council for Diamonds discovered fraud in certificates. Certificates were forged so that diamonds could be sold at higher prices.

Diamonds are formed under high pressure at a depth of between 140 and 190 kilometres in the earth’s mantle by compressing carbon. They are brought to the earth’s surface by rapid transport by means of explosive volcanoes. The volcanic rock has a characteristic blue colour and is called kimberlite after the place Kimberley in South Africa. In the nineties of the 20th century there was a diamond rush in northern Canada after the discovery of a kimberite pipe with economically recoverable diamonds in Lac de Gras in 1991.

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In addition to deposits in kimber loopt pipes and their immediate surroundings, diamonds also occur in alluvial deposits. In India, the delta of the river Krishna was traditionally the site of alluvial diamonds. Alluvial diamonds are also found in the Sperrgebiet south of Lüderitz on the coast of Namibia and in the adjacent coastal area of South Africa. In these areas, diamonds can be found in a sand layer up to a few metres below the surface. These areas are closed to anyone who has no business there. Part of the diamond is also washed into the Atlantic Ocean and is mined there by diamond fishermen.

High-pressure subduction zones may function as an alternative parent rock for diamonds. In the Beni Bousera massif in northern Morocco, micro diamond associations have been found that point in that direction.

The table below shows an overview of the diamond production since 2006. In 2009 production decreased by about 20% as a result of the credit crisis. Production has not yet recovered to pre-crisis levels. Until 2007 South Africa was the fifth largest producer worldwide, but in that year it was pushed to the sixth position by Canada. In 2016 the average value of a carat rough diamond was US$ 92.50. Diamonds with the highest value per carat were mined in Lesotho, average value over US$ 1000, and in the Democratic Republic of Congo (DRC) this was only US$ 10. The latter country had a share of 17% in global production in volume terms, but in value terms this share was 2%.

The Russian company ALROSA, active in the republic of Yakutia, is the largest producer of diamonds in the world with 28% of world production. De Beers, which for a long time had a virtually world monopoly on diamonds, is the second player with 20% of production. Rio Tinto is number three with a share of 17%. In Australia Rio Tinto is the largest producer of coloured diamonds in the Argylemine in the Kimberley area. In Angola Catoca is still a major producer, ALROSA has a 32.8% stake in this company.

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A diamond appearance is economically viable if there is at least 1 carat of gemstone quality per ton of stone present.

In addition to gemstone quality, an occurrence in practice provides a multiple of low quality diamonds. This diamond finds its way as an industrial diamond, used for drilling and sawing. Annually about 130 million carats of diamonds are mined, of which about 80% are industrial diamonds.

In addition, 570 million carats (110 tons) of synthetic diamonds are produced annually for industrial use. Approximately 90% of all diamond cutting powder today is synthetic. The majority of synthetic diamonds are still produced under high pressure. A growing proportion is produced by evaporation at low pressure. The small crystals produced by this technique are used as an ultra-hard coating in the manufacture of preformed tools.