The diamond is one of many allotropes can present carbon; in particular the diamond is made up of a crystalline lattice of carbon atoms arranged in a tetrahedron structure.
Diamonds are thought to have been initially recognized and extracted in India, where they were found in alluvial deposits along the Krishna and Godavari rivers . The diamonds were used in religious icons and are likely to be known and considered valuable already 6,000 years ago. Indeed, references to diamonds are found in Sanskrit texts: Kautilya’s Arthashastra mentions commerce, Buddhist works from the 4th century BC, and then describes the diamond as a very valuable and precious stone, although it does not contain any indication of cutting techniques.
Another Indian text written at the beginning of the 3rd century describes the resistance, regularity, brilliance, scratchiness of metals, and good refractive properties as desirable qualities of a diamond.
The Indian city of Golconda was for centuries and until the mid-nineteenth century the main diamond production and sale center, so that its name was synonymous with wealth.
The diamonds arrived in ancient Rome from India and there are clear references to their use as engraving tools.
The Chinese, who did not find diamonds in their country, did not consider them in the past as jewels as they appreciated the jade. A Chinese work of the 3rd century BC cites: “Foreigners wear ” diamonds ” in the belief that they may turn away from them malignant influences.”
Until the 18th century diamonds came exclusively from India or Borneo and only in 1725 in Brazil, in the State of Minas Gerais, the first diamonds from South America were found. Then, in 1843, carbonado was found, a black-and-black microcrystalline diamond aggregate used in industry.
The first find in South Africa took place in 1867, near the sources of the Orange River, and until 1871 only the alluvial fields were exploited. Later, the existence of diamond diamond fireplaces was discovered, of which the most well-known is the Kimberley mine which has named the diamond core rock, the kimberlite.
In the eighteenth century, finds were discovered in the Borneo area, this began the diamond trade in Southeast Asia. With the exhaustion of Indian resources, significant discoveries took place in Brazil (1725) and South Africa (Kimberley, 1867). South Africa therefore became the world’s leading center for the production of this precious gem.
The popularity of diamonds has increased since the nineteenth century thanks to the greater supply, the improvement of cutting and polishing techniques, the growth of the world economy and also thanks to successful advertising campaigns. 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 combustion product was carbon dioxide, thus proving that the diamond is a carbon compound. He then showed that at a temperature of about 1,000 ° C, in a non-oxygenated environment, the diamond turned into graphite.
Origin and dating
The diamonds originate in the Earth’s mantle , where the very high pressure conditions necessary for their formation exist. It is thought that the diamonds found on the surface come from a depth of 150 to 225 km. The crystals are brought to the surface, embedded in a rock containing a lot of olivine called kimberlite, by volcanic ducts through eruptions. This gives rise to diamond diamond fireplaces of the primary fields. Subsequently, by erosion, kimberlite may crumble, releasing diamonds in secondary fields, generally of an alluvial type.
Very small diamonds, typically smaller than 0.3 mm in diameter, have been found in many meteorites that have fallen on Earth. Some scholars believe that the impacts of large meteorites that occurred millions of years ago may have produced some (or many) of the diamonds that have been found today, but there is no evidence to support this hypothesis.
The carbon-14 method is not effective for diamond dating because it is limited to carbon of biological origin. Geocronography techniques are also ineffective for this reason, because of the chemical purity of the diamond. Geologists, however, believe that most of the diamonds found, that is, those formed in the cloak and came to the surface, formed between about 1 and 1.6 billion years ago.
Diamonds are the crystallized modification of pure carbon ; since they have been formed, like oil, in millions of years, they are an exhalable mineral. The diamond crystals can be shaped like an octahedron or a hexamethasone, sometimes with curved faces. Sometimes, on the octagonal faces, there are trunks, ie triangular engravings. Some gemmations can lead to flat crystals in the shape of a triangular bevel. Other forms in which are present are the rombododecaedri and the cubes; however, fewer are the esacisottairs, cubic and dodecahedral crystals. There are also missing gemini crystals or tetrahedral symmetry.
Forms in which it is presented in nature
The color is varied, as well as the size of the crystals that very rarely exceed those of a hazelnut. The magnitude record for a rough diamond belongs to the diamond Cullinan, found in 1905 in the Premier Mine of South Africa. Perfect in clarity and color, weighed 3.025 carats (605 grams); cut in 105 machined stones, the largest weighs 516.5 and 309 carats (up to 1988 the largest diamonds worked). Currently the largest diamond worked is the Golden Jubilee of 545.67 carats, found in 1985 in South Africa.
The diamond amber fields are divided into two groups: primary and secondary. The primary deposits are those in which the diamonds are still within the mother rock (typically, the kimberlite), while the secondary fields are those in which they are dispersed in sedimentary rocks often inconsistent type sand, gravel, transported away from places where the parent rock was located and from which they stem for its disintegration, that is, in alluvial soils.
In the case of the primary fields, the rock is extracted into smaller pieces, alternating the abundant wash splits so that the water separates gang from the heaviest 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 ” or ” well ” (unlike coal mines, where mining is often done in tunnels excavated in depth). Among the most famous diamond mines are Kimberley and Premier Mine, both in South Africa. The mines near Golconda in India have provided up to the mid-nineteenth century almost all the diamonds produced in the world.
In the alluvial fields , without having to smudge the rock, the process is simpler: only the gravitational process with water is used, dropping the diamonds in the tanks. Then diamonds and ganga residues are removed from grease-fed rolls, to which diamonds and ganga adhere. The ganga is then slipped off by other washing. Then, to remove the diamonds from the fat, the whole mixture is fused; the fat melts, releasing the rough diamonds. They are then divided into two groups: of superior quality, that is, gemmological (suitable to be cut and polished to produce jewelery) and inferior quality, suitable for industrial applications.
It is estimated that the primary mines produce on average a diamond carat (0.2 grams) of every 3.5 to 4 tons of rock extracted, while only one carat is extracted from the alluvial fields, each about 15 tons of material.
The world-wide production of natural diamonds varies considerably from year to year, because diamonds are often sold out quickly, and mining continues in new mines that can produce very different productions. In 2010, world diamond production was about 224 million carats (about 44,800 kg).
The value of rough diamonds varies enormously depending on whether they are of gemological or industrial quality. In 2010, the largest producers of diamonds of gem quality were the following: Botswana 25,000,000 carats, Russia 17,800, Angola 12,500, Canada 11,770, Congo (Kinshasa) 5,500. Brazil also produces remarkable quantities. South Africa has in the past been one of the largest producers, but in recent years production is almost exclusively of industrial quality diamonds. Australia up to 2006 has produced remarkable amounts of gemological diamonds, but following the exhaustion of its origins, it is not currently among the top ten producing countries. Until the end of the nineteenth century almost all the diamonds were extracted in India, but later the mines were gradually depleted. Diamond extraction in India is almost exclusively done in the District of Panna, in the state of Madhya Pradesh.
As far as industrial quality diamonds are concerned, the major producing countries in 2010 were: Congo (Kinshasa) 22,200,000 carats, Russia 15,000, Australia 9,900, Botswana 7,000, South Africa 5,400. 
Altogether, about half of the diamonds extracted today in the world come from mines located in central and southern Africa. DeBeers South Africa, based in Johannesburg, controls almost all the extraction, processing and marketing of diamonds of African origin. Among the world’s largest diamond mining companies, there is also the Anglo-Australian BHP Billiton.