Diamonds' history

diamonds' history

Diamond is one of the many allotropic forms in which carbon can appear; in particular, the diamond is constituted by a crystalline lattice of carbon atoms arranged according to a tetrahedral structure.
It is thought that diamonds were initially recognized and extracted in India, where they were found in alluvial deposits along the Krishna and Godavari rivers. Diamonds were used in religious icons and are likely to be known and considered precious as early as 6,000 years ago. [1] In fact there are references to diamonds in Sanskrit texts: the Arthashastra of Kautilya mentions the trade, [2] Buddhist works from the 4th century BC. onwards they describe the diamond as a very well-known and precious stone, even if they do not contain indications about cutting techniques. [3]

Another Indian text written at the beginning of the third century describes strength, regularity, brilliance, the ability to scratch metals and good refractive properties as desirable qualities of a diamond [4].

The Indian city of Golconda was for centuries and until the mid-nineteenth century the main center of production and sale of diamonds, so that its name was synonymous with wealth.

Diamonds came to ancient Rome from India and there are clear references to their use as engraving tools. [5] [6]

The Chinese, who did not find diamonds in their country, did not consider them as jewels in the past, while they appreciated jade a lot. A Chinese work of the III century BC he quotes: "Foreigners wear them [diamonds] in the belief that they can remove evil influences from them". [4]

Until the eighteenth century the diamonds came exclusively from India or Borneo and only in 1725 in Brazil, in the State of Minas Gerais, were found the first diamonds from South America. Later, in 1843, carbonado was found, a diamond-black microcrystalline aggregate, used in industry.

The first discovery in South Africa occurred in 1867, near the sources of the Orange River, and until 1871 only alluvial deposits were exploited. Later it was discovered the existence of the diamond chimneys, of which the best known is the Kimberley mine which gave its name to the mother rock of the diamond, the kimberlite.

In the eighteenth century deposits were discovered in Borneo, which began the diamond trade in Southeast Asia. With the depletion of Indian resources, significant discoveries took place in Brazil (1725) and South Africa (Kimberley, 1867). [7] South Africa therefore became the main world center for the production of this precious gem. [7]

The popularity of diamonds has increased since the nineteenth century thanks to the increased supply, the improvement of cutting and polishing techniques, the growth of the world economy and also thanks to innovative successful advertising campaigns. [8] In 1813 Humphry Davy used a lens to concentrate the sun's rays on a diamond in an oxygen environment and showed that the only product of combustion was carbon dioxide, proving that the diamond is a carbon compound. He later demonstrated that at a temperature of about 1,000 ° C, in an oxygen-free environment, the diamond converts to graphite. [9]

Origin and dating

Diamonds originate in the mantle of the Earth, where the conditions of high pressure necessary for their formation exist. It is thought that the diamonds found on the surface come from a depth between 150 and 225 km. [10] The crystals are brought to the surface, embedded in a rock containing a lot of olivine called kimberlite, from volcanic conduits by eruption. This gives rise to the diamond chimneys of the primary deposits.Later, by erosion, kimberlite can be broken down, freeing diamonds in secondary deposits, generally alluvial. [11]
Very small diamonds, typically with a diameter of less than 0.3 mm, have been found in many meteorites that have fallen to Earth. Some scholars believe that impacts of large meteorites, which occurred millions of years ago, may have produced some (or many) of the diamonds found today, but there is no evidence to support this hypothesis. [12]

The carbon-14 method is not effective for diamond dating because it is limited to carbon of biological origin. Also due to the chemical purity of the diamond, also the techniques of geochronology are ineffective for this purpose. However, geologists believe that most of the diamonds found, ie those formed in the mantle and arrived at the surface, were formed between about 1 and 1.6 billion years ago. [13]  

Diamonds are the crystallized modification of pure carbon; since they have been formed, like oil, over millions of years, they are an exhaustible mineral. Diamond crystals can be in the form of an octahedron or an esacisottahedron, sometimes with curved faces. Sometimes on the sides of the octahedron there are trines, or triangular incisions. Some buds can lead to flat crystals in the shape of a blunt triangle. [11] Other forms in which it appears are the rhombododecahedra and the cubes; however less rare are the esacisottaedric, cubic and dodecahedral crystals. There are also twin crystals or tetrahedral symmetry. [14]
The color is varied, as is the size of the crystals that very rarely exceed those of a hazelnut. The record of greatness for a rough diamond belongs to the Cullinan diamond, found in 1905 in the Premier Mine of South Africa. Perfect in its clarity and color, it weighed 3,025 carats (605 grams); cut into 105 worked stones, the largest weigh 516.5 and 309 carats (up to 1988 the largest worked diamonds). Currently the largest diamond worked is the Golden Jubilee of 545.67 carats, found in 1985 in South Africa.

extraction

The diamond deposits are divided into two groups: primary and secondary. The primary deposits are those in which the diamonds are still found inside the mother rock (typically, the kimberlite), while the secondary ones are those in which they are dispersed in sedimentary rocks often incoherent such as sand, gravel, transported away from the places where the mother rock was located and from which it derives due to its disintegration, that is to say in alluvial lands.

In the case of primary deposits it is necessary to crush the rock extracted into smaller and smaller pieces, alternating the splits with abundant washes so that the water separates the gangue from the heavier materials; the relatively high specific weight of the diamonds causes them to fall into the tanks below (possibly mixed with other heavy minerals).

Most diamond mines are "open air" or "well" (unlike coal mines, where mining often takes place in tunnels dug deep). The most famous diamond mines are those of Kimberley and Premier Mine, both in South Africa. Until the mid-nineteenth century, the mines around Golconda in India provided almost all the diamonds produced in the world.

In alluvial deposits, not having to chop the rock, the process is simpler: only the gravitational process with water is used, dropping the diamonds into the tanks. Afterwards the diamonds and gangue residues are taken away by rollers sprinkled with grease, to which the diamonds and the gangue adhere. The gangue is then slid away by other washes. Subsequently, to remove the diamonds from the fat, the whole mixture is melted; the fat melts, thus freeing the rough diamonds. They are then divided into two groups: superior quality ie gemological (suitable to be cut and polished to produce jewelry) and of inferior quality, suitable for industrial applications.

It is estimated that the primary mines produce an average of one carat of diamonds (0.2 grams) every 3.5 - 4 tons of rock extracted, while from the alluvial deposits one carat is extracted every 15 tons of processed material. [15]

producer countries

The world production of natural diamond varies considerably from year to year, because the diamond strands are often sold out quickly, and the extraction continues in new mines discovered, which can give very different productions. In 2010 the world production of natural diamonds was about 224 million carats (equal to about 44,800 kg).

The value of rough diamonds varies enormously depending on whether they are of gemological or industrial quality. In 2010 the major diamond-producing countries of gemological quality were the following: Botswana 25,000 thousand carats, Russia 17,800, Angola 12,500, Canada 11,770, Congo (Kinshasa) 5,500. Brazil also produces considerable quantities. South Africa has in the past been one of the major producers, but in recent years production is almost exclusively of industrial grade diamonds. Until 2006, Australia produced significant amounts of gemological diamonds, but following the exhaustion of the strands it is not currently among the top ten producing countries. Until the end of the nineteenth century almost all the diamonds were mined in India, but later the mines gradually ran out. The diamond mining in India today takes place almost exclusively in the Panna District, in the State of Madhya Pradesh.

As far as industrial grade diamonds are concerned, the major producer countries were the following in 2010: Congo (Kinshasa) 22,200 thousand carats, Russia 15,000, Australia 9,900, Botswana 7,000, South Africa 5,400. [16]

Overall, about half of the diamonds today extracted in the world come from mines located in central and southern Africa. The South African company DeBeers, based in Johannesburg, almost completely controls the extraction, processing and marketing of diamonds of African origin. The Anglo-Australian BHP Billiton is among the world's largest diamond mining companies.

diamonds from jewelry

Thanks to its hardness, the diamond can be scratched only by other diamonds and is able to preserve the polishing for long periods of time: it is therefore suitable to be worn daily withstanding very good wear, and is therefore widely used in jewelry .

Cut
Cutting rough diamonds to turn them into jewelry gems is a very delicate and difficult operation. Any errors would lead to the loss of substantial sums of money. The most common form of diamond cutting is that round, called a brilliant. This term identifies a round cut with at least 57 facets, to which a lower table (not always existing) is added.

The great diffusion of this cut has led to a misunderstanding: the public tends to identify the terms brilliant and diamond as if they were the same thing. In reality, the term bright, if used alone, identifies only a stone with a round cut, also synthetic. All gems can be cut to brilliant, such as rubies, sapphires, quartzes and topazes, but the aesthetic result is very different due to the different indices of refraction.

Other types of cutting, among the most popular and widespread are: the cut to heart, bright oval, marquise or navette, huit-huit, drop, emerald, carré, baguette, trapeze, Dutch rose, with rosette (now in disuse). [25] To remember other more recent cuts that are slowly affirming in the field of jewelry: the princess, the radiant, the barion and the cushion.

The largest diamond-cutting center has long been the city of Antwerp in Belgium, where more than 12,000 technicians and employees of cutters, polishers and salespeople are still working in the Diamantkwartier (diamond district). Recently, however, the Indian city of Surat has been imposed worldwide for cutting. It is estimated that currently over 80% of diamonds (especially the small ones) are cut in this city [26]. Other important centers are Tel Aviv and New York. Some companies, in particular De Beers, have their own cutting centers, but they often rely on external clippers that are particularly expert in cutting diamonds of the highest value.

https://it.wikipedia.org/wiki/Diamante#Cenni_storici