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| | Sometimes, both impact and metamorphic diamonds form rather large-scale deposits with huge stocks and in high concentration. But, diamonds in these types of deposits are so small that they have no industrial value.
Commercial diamond deposits are connected with kimberlite and lampro lamproit pipes, dating back to ancient cratons. Main deposits of this type are known in Africa, Russia, Australia and Canada.
According to the estimation of company "De Beers", the following are the leading countries in diamond mining ( in terms of value) in 2004:
* Botswana — 2.9 Billion USD;
* Russia — 2 Billion USD;
* Canada — 1.4 Billion USD;
* South Africa — 1.3 Billion USD;
* Angola — 1.2 Billion USD;
* Namibia — 0.7 Billion USD.
It is considered that the first synthetic diamond was made by Henri Moissan.
In 1961, the first publications of the firm "DuPont" were published about the realization of ideas for obtaining diamonds by the direct phase transition from graphite. The synthesis was carried out by using explosion energy.
At present, the large industrial production of synthetic diamonds exists, which ensures the requirements in abrasive materials.
Several methods are used for synthesis. One of the methods is the preparation of high carbon alloy “nickel-manganese” and its cooling under pressure in forms, made from solid alloy (type VK). Crystallized tiny diamonds are separated after dissolving the metallic dust in the mixture of acids.
The modern methods of obtaining diamonds use gas mediums consisting of 95 percent hydrogen and 5 percent carbonaceous gas, propane, acetylene and also high-frequency plasma, concentrated on the substrate where the diamond is formed. The temperature of the gas ranges from 700—850 degrees when the pressure is thirty times less than the atmospheric pressure. Depending on the synthesis technology, the growth rate of diamonds can be from 7 microns per hour to 3 microns per minute on substrate.
The hydrothermal method of the build-up and growth of diamonds uses a mixture of nitric, sulfuric and acetic acids and also graphite at an optimum temperature of 50oC and atmospheric pressure.
Already for several centuries, the diamond is the most popular and expensive precious stone. While the price of other precious stones is determined by fashion and constantly varies, the diamond remains stable in the booming precious stone market. To a considerable degree, such a steady position of the diamond is due to the high monopolization of this market. The firm "De Beers ", which holds roughly 50% of world production, mines deposits in Botswana, the Republic of South Africa, Namibia and Tanzania.
The exclusive toughness of diamond finds applications in industry: knives, drill bits, cutters and similar products are made from diamonds. Diamond powder (both waste obtained during the processing of natural diamonds, as well as ones obtained artificially) is used as an abrasive.
However, the overwhelming part (with respect to cost) of natural diamonds is used for the production of cut-diamonds.
The main cutting types are: round (with standard number 57 sides) and fantasy. The following cutting types belong to fantasy: "oval", "pear" (one side oval — sharp corner), "marquise" (“oval with two sharp corners”, which is similar to the stylized image of an eye), "princess", "radiant" and so on.
The shape of the faceting of a cut-diamond depends on the shape of the raw crystal of the diamond. To obtain diamonds of maximum cost, cutters try to reduce the loss of a diamond to a minimum during processing. Depending on the shape of the crystal of a diamond, approximately 55% to 70% weight is lost during processing. Proportionally the price (but not the cost!) of the cut diamond increases. Hence, at 50% “vendible output”, a cut-diamond weighing 0.5 carats with a cost 100 USD (considering only the costs on raw materials without other miscellaneous expenses) with a price tag of 200 USD per carat is obtained from the diamond weighing 1 carat, the cost 100 USD and the price tag of 100 USD.
With respect to processing technology, diamonds can be conventionally divided into three big groups: — first, as a rule, crystals of a regular octahedral shape, which are cut initially into two parts, that can be used as blanks for the manufacture of two cut-diamonds; — makable (crystals of an irregular or round shape, which are subjected to cutting a “single piece”); — cleavage (containing a crack and are not cut but cleaved before further processing).
The main diamond cutting centers are: India, specializing predominantly on small cut-diamonds, weighing up to 0.30 carats and produces roughly 7 billion dollars worth diamonds per year; Israel, cut-diamonds weighing more than 0.30 carats and produces approximately 2.5 billion dollars per year, China, Russia, Thailand, Belgium and the USA. Production in the last five enlisted countries stands at 0.5-1 billion dollars In this case, only large high-quality cut-diamonds are produced in the USA, small cut-diamonds are produced in China and Thailand and the average and large cut-diamonds are produced in Russia and Belgium. Similar specializations were formed due to the distinctions in labor remuneration to the cutters.
On April 11, 2006, Christies Auction House in New York will hold its Magnificent Jewels sale. At the sale, Christies will offer diamonds from the collection of Joan Kroc, whose husband founded the McDonald's chain of fast food restaurants. One of the items that will be included in the collection will be a pear-shaped (D.IF) 50.53-carat diamond. This diamond is set in a ring and flanked on either side by more pear-shaped diamonds. Of the natural colored diamonds that will be offered for auction at the Magnificent Jewels event, one ring set offers pear-shaped fancy dark blue-gray diamond within a pave-set pink diamond surround of approximately 14.43 carats with an estimated value of $1.2-$1.5 million. Other colored diamonds in the expansive collection include: Fancy intense blue, internally flawless diamond of 3.17 carats with an estimated value of $500,000-$700,000) and a modified square-cut fancy pink diamond of approximately 5.25 carats set in a ring and flanked on either side by a trapeze-cut diamond with an estimated value of $400,000 - $600,000.
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