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While the formation of diamonds may still be largely a mystery, one thing is know precisely - where on the earth's surface they occur: in kimberlite, a type of rock named after the South African town of Kimberley, where it was first identified in 1880.

Kimberlite is the heterogeneous product of a chaotic genesis, for this is the rock which was explosively transported through the "pipes" out of the earth's mantle to the top. Besides solidified magma of varying composition, kimberlite contains fragments of rock which it carried along on its impetuous journey.

Deposits of diamond-bearing kimberlite, which were found in Africa, Brazil, India, Australia, North America and Sibiria, occur only in the oldest and most stable continental regions, far removed from the restless zones where the rigid plates making up the earth's crusts move away from each other, scrape along each other or collide. Under these old, undisturbed continental plates, the so-called "shields", the crust is thickest, its weight generating pressures high enough to produce diamonds in the upper regions of the mantle, the place of origin of the kimberlite.

Many kimberlite deposits formed 70 to 150 million years ago; indeed, some of those found were up to 1.2 billion years old. As the kimberlite probably contained large amounts of solid rock, it did not spurt from the fissures in the earth's surface like liquid lava. Rather, the pressure of the rising magma probably resulted in the surface rock bulging upward and then collapsing in the centre when the gasses driving the kimberlite had escaped. In the thus formed crater it solidified to a rock deposit with a diameter of a few hundred metres to 1.5 kilometres. Here the primary deposits of diamonds had formed, i.e. the diamonds are at the place where they had originally risen to the earth's surface (opp.: secondary deposit).

Like any other category of rock on the surface of the earth, these craters, too, were attacked by water, wind, ice or chemicals of the atmosphere. Through this they are flattened and eroded, producing the so-called "yellow ground". This is the kimberlite weathered by the above-named influences, in which the first diamonds from primary deposits were found in South Africa. The unweathered kimberlite beneath it, "blue ground", was not recognised as diamond-bearing until later.

Gravity, wind and water carry off the fragments of the craters and deposit them, often over long distances, as sediments into river beds, alluvial plains and on the bottom of the sea. While rock is worn down through the slow process of erosion, the much harder diamonds , which are not crushed even through the extremely long-lasting rolling and pushing, remain undamaged and are slowly washed downstream.

There they accumulate gradually in the so-called alluvial deposits. These secondary deposits are usually richer, more concentrated deposits than the primary deposits, having already undergone a screening process: The rock surrounding the diamonds, because it is softer and lighter, is swept away farther, but the diamonds stay put.

Global distribution of the diamond depositsHere is an overview of the global diamond deposits: Overview.Historically, the diamond deposits in India were the first to be exploited. It is here that most of the historic diamonds originated. The major deposits are mainly found in the eastern parts of the country. Until the discovery of the first diamonds in Brazil, India alone supplied the world diamond demand; it is estimated that 30 million carats worth of rough diamonds had been extracted here up to this time. Then the Brazilian diamond deposits were discovered at the beginning of the 18th century. These were mainly encountered near rivers (secondary deposits). The finds made there were so rich that the trade from India almost came to a standstill.

The quantities arriving in Europe from Brazil at that time amounted to about ten times the Indian production. Brazil was the world's main supplier for the continuously growing diamond demand for almost 150 years. After 1850 its diamond stocks slowly ran out - again the trade almost stopped. Luckily, however, it was at that time that the first finds were made in South Africa.

The reason why these were so important was that they were the first primary diamond deposits discovered (previously, only secondary deposits had been known), and that they were, firstly, extremely productive ( by 1880 the South African finds had already increased the rough diamond production to three million carats ), and, secondly, laid the foundation for the de Beers group's global position of power which continues to this very day. In this period the diamond reached a share of more than 80% of the world-wide precious stone sales (that is why it was called "king of the precious stones"). This naturally entailed risks for the price so that special politico-economic measures became necessary in order to maintain the relative rarity of the diamond, even if, on average, only a quarter of the overall output was suited for gemstones.

A central marketing organisation for the major part of the South African rough diamonds was set up to align supply with demand via an adjustment of the output. The forerunner of today's Central Selling Organisation of De Beers had been set up.To date, the 20th century brought further discoveries of African diamond deposits (Africa's currently 13 diamond-producing countries lead world diamond production with a share of about 70%). The share of gem-quality diamonds is exceptionally high in Namibia, at 90 - 95 % (mainly secondary deposits from the pipes of South Africa).

See also: Example for the importance of diamond production in the Third World.Meanwhile, Russia has developed into one of the largest diamond producers. It was not until 1949 that the deposits there were seriously worked. Extensive alluvial deposits in Sibiria, future diamond-bearing pipes, soon will let Russia rise to one of the top places in the world ranking list of diamond suppliers. . China, too, now belongs to the major diamond countries.

The first deposits (primarily alluvial ) are discovered from 1940; later the great breakthrough is achieved - with the discovery of several kimberlite pipes. The almost spectacular deposits in Australia must be mentioned: Since 1986 the Argyle-Mine there, in the northwest of the continent, has been in full production, and in 1994 production had already risen to thirty-nine million carats. That corresponds to roughly a third of the world production, and first place. But this needs to be relativised by the fact that the share by value is hardly a tenth of it. For, only 5% of the total production are diamonds with good gem quality (gemstones), 45% with inferior gem quality and 50% industrial diamonds.In North America several finds were made, including pipes, but none of major importance. For the future, however, a large diamond production may be expected in Canada.

rough diamondin kimberlite

Drawings ex: "Edelsteine und Schmucksteine: alle Edel- und Schmucksteine der Welt", Walter Schumann, 10. , neubearb. Aufl., Munich, Vienna, Zurich: BLV, 1995