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| | Sometimes, both impact and metamorphic diamonds form rather large-scale deposits with huge stocks and 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 estimation of company "De Beers", the following are 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, first publications of the firm "DuPont" were published about realization of ideas of obtaining diamonds by direct phase transition from graphite. Synthesis was carried out by using the explosion energy.
At present, large industrial production of synthetic diamonds exists, which ensures requirements in abrasive materials.
Several methods are used for synthesis. One of the methods is 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.
Modern methods of obtaining diamonds use gas medium consisting of 95 percent hydrogen & 5 percent carbonaceous gas, propane, acetylene and also high-frequency plasma, concentrated on substrate, where diamond is formed. Temperature of gas ranges from 700—850 degrees when the pressure is thirty times lesser than the atmospheric pressure. Depending on synthesis technology, growth rate of diamonds from 7 micron per hour to 3 micron per minute on substrate.
Hydrothermal method of build-up and growth of diamonds uses mixture of nitric, sulfuric and acetic acids and also graphite at optimum temperature of 50oC and atmospheric pressure.
Already for several centuries, diamond is the most popular and expensive precious stone. While the price of other precious stones is determined by fashion and constantly varies, diamond remains stable in booming precious stone market. To a considerable degree, such steady position of diamond is due to high monopolization of this market. Firm "De Beers ", which holds roughly 50% of world production, mines deposits in Botswana, Republic of South Africa, Namibia and Tanzania.
Exclusive toughness of diamond finds applications in industry: knives, drill bits, cutters and similar products are made from diamonds. Diamond powder (both wastage , obtained during the processing of natural diamond, as well as obtained artificially) is used as abrasive.
However, overwhelming part (with respect to cost) of natural diamonds is used for production of cut-diamonds.
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 stylized image of an eye), "princess", "radiant" and so on.
Shape of the faceting of cut-diamond depends on the shape of raw crystal of diamond. To obtain diamond of maximum cost, cutters try to reduce the loss of diamond to a minimum during processing. Depending on the shape of crystal of diamond, approximately 55% to 70% weight is lost during processing. Proportionally, the price (but not the cost!) of cut-diamond increases. Hence, at 50% “vendible output”, cut-diamond weighing 0.5 carat with cost 100 USD ( considering only costs on raw materials without other miscellaneous expenses) with price tag of 200 USD per carat is obtained from diamond weighing 1 carat, cost 100 USD and 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 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 irregular or round shape, which are subjected to cutting “single piece”); — cleavage (contain crack and are not cut but cleaved before further processing).
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 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 USA, small cut-diamonds are produced in China and Thailand and average and large cut-diamonds are produced in Russia and Belgium. Similar specialization was formed due to the distinctions in labor remuneration to 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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