Story of the Diamond

World Diamond Group

Origin of the word Diamond

The word “diamond” is derived from the Greek “damas” which means untameable. Already in the first century AD, the diamond was mentioned in the Natural History of Plinio the Elder, who considered it the most precious stone and harder than all the other stones. For this reason it assumes an important symbolic significance and is linked to the capacity to ward away evil via its incorruptibility.

The diamond represents one of many forms of carbon. In this case the atomic composition of carbon is made in the geometric shape of an octahedron.

Story of the Diamond

The story of the diamond begins in India, rich in deposits around the rivers Krishna, Godavari and Penna. Generally diamonds were used in religious symbols, and have for many centuries been considered precious. Buddhist writings of the 4th century BC, defined the diamond as a precious stone. Other writings in India mentioned the capacity of the diamond to scratch metal, and referred to its brilliance and its capacity to reflect light.

The first references to the use of the diamond in Ancient Rome come from India. The Romans used it as an instrument of incision because of its hardness. In China diamonds were mentioned as a talisman with the power to drive away evil. The extraction of diamonds up to the 18th century was in river deposits, above all in India , and later the first diamonds were found in Brazil, and elsewhere in South America. Only later, in 1867, were the first diamonds discovered in South Africa.

The discovery of diamonds in South Africa was linked to the paths of exhausted volcanos. They were found in Kimberley, which gave its name to the rock from which diamonds are extracted, namely kimberlite. After this discovery South Africa became an important centre for the extraction of diamonds, and at the global level, substituted for India which had exhausted its own centres of extraction.

Diamonds gained more prominence in the 19th century, which coincided with improvements in gem cutting techniques. Only in 1813, thanks to an experiment by Humphry Davy, who focused with a lens beams of sunlight on a rough diamond triggering combustion, was it possible to see the chemical composition of the carbon. This discovery contributed to increase the fame of the diamond and its peculiar characteristics. Carbon at extraordinarily high pressures many millions of years ago, had created the hardest stone that had ever existed in nature.

Origin of the diamond

The diamond was formed millions of years ago in the earth’s crust and only thanks to volcanic eruptions emerged on the earth’s surface in kimberlite. The erosion and crumbling away of kimberlite freed diamonds of various sizes, colours and purities, which would later be sorted in specialised centres. One of the most important diamonds discovered in the kimberlite deposits was the Cullinan, found in 1905 at the Premier mine.

The Cullinan diamond weighed 3,025 carats in its rough form, equivalent to 605 grammes. After it was cut around 100 stones were obtained, of which the most important weighed 516.5 carats.

Diamond deposits

The extraction of diamonds could take place in two types of deposit: primary and secondary. In the primary deposits, diamonds are found in kimberlite and are extracted by crumbling it away, while in the secondary they are found around river deposits, in the sand or gravel or in the rivers.

Normally to extract one carat of diamond requires processing 5 tonnes of kimberlite, or sifting through some 20 tonnes of sand in river deposits.

The chemical composition of the diamond

The structure of a diamond is composed of crystals that will form an octahedron. Based on the gemmation of the carbon crystals, various shapes are found, whether triangular, or more rarely cubic shapes.

As mentioned in the previous chapter, the diamond is a crystal composed of carbon atoms that combine in the structure of a tetrahedron. Among the characteristics that are most important, one can mention the fusion point which is 3,820 degrees Kelvin, the index of refraction of light, and the hardness index which is equal to 10 on the Mohs scale.

Chemical-physical properties

The diamond is a transparent crystal composed of carbon atoms in a tetrahedron structure. Diamonds have diverse applications, thanks to the exceptional physical characteristics of the material from which they are made. The most relevant characteristics are extreme hardness, the index of refraction of light, high thermal conductivity, with a fusion point of 3,820 K.

Hardness

The diamond is the hardest known mineral. Its hardness as measured on the Mohs scale (an empirical gauge of the hardness of materials) is equal to 10, and is due to the presence of extended links throughout its atomic structure. This explains the exceptional characteristics of stability of this structure, and of similar structures with similar characteristics, for example boron nitride.

Among materials of synthetic origin are ADNR (Aggregated Diamond Nanorods), a form of carbon synthesised for the first time in 2005 by researchers of the German university of Bayreuth, Natalia Dubrovinskaia, Leonid Dubrovinsky, and Falko Langenhorst. Beside having other notable properties, this material turned out to be harder than a natural diamond. 

Not all diamonds have the same hardness. The hardest diamonds are from the area of New England in New South Wales (Australia.) These diamonds are generally small, have a perfect or semi-perfect octahedron shape, and are used to polish other diamonds. Their hardness is considered to be the result of the way in which the crystal grew, in a single phase. Most other diamonds demonstrate crystal growth in successive phases, with inclusions of impurity and the formation of defects in the crystalline lattice and consequent diminution of the characteristics of hardness.

Conductivity

Esistono o sono allo studio altre applicazioni specialistiche, compreso l'uso come semiconduttore: alcuni diamanti blu sono semiconduttori naturali, a differenza degli altri diamanti che invece sono eccellenti isolanti elettrici. Il diamante esposto all'aria mostra in alcune condizioni un comportamento da conduttore sulla sua superficie. Il fenomeno venne scoperto da Maurice Landstrass e K. V. Ravi nel 1989.

Nel dicembre 2007 un laboratorio del Case Western Reserve University di Cleveland ha dimostrato che la conducibilità avviene per mezzo di un film acquoso sottile deposto sulla superficie del diamante. Il film d'acqua scambia coppie di elettroni con la superficie rendendola conduttrice. Il diamante si dimostra un ottimo conduttore termico ma ad alta temperatura tende a decomporsi in semplice carbonio.

Placing a date on a diamond

The carbon-14 method is not efficient in this case, because it is limited to carbon of biological origin. Also techniques of geochronology, for example, the uranium-lead method, are inefficient in this respect, because of the chemical purity of the diamond.

Diamonds in jewellery

The diamond became important in jewellery due to its capacity to preserve its polished appearance for long periods. Only a diamond is capable of scratching another diamond, and so it can be worn every day without worrying about suffering any damage.

The round shape of the diamond is the most famous and most widely used in the world of jewellery. The brilliant diamond cut indicates a diamond with 57 facets. The great popularity of this cut has led to a misunderstanding: the public tends to identify the terms brilliant and diamond as if they are the same thing. In practice the term brilliant, if used alone, only identifies the diamond with the round cut. There are, however, many other precious stones that can have a brilliant cut, for example topaz, rubies and sapphires.