Diamonds are a special crystallization form of carbon atoms. Carbon is nature’s principal building block: plants, animals and mankind too consist of carbon compounds. Diamond crystals came into existence about 3 billion years ago, at a depth of 140 to 200 kilometres inside the earth; they originated from carbon which was exposed to very high pressure (up to 70,000 kg per cm²) at a very high temperature (up to 2000 degrees Celsius).

Origin and extraction

Rough diamonds are found in three places:

1. At a depth of 140 to 200 kilometres inside the earth. From there the diamond-bearing rock, called kimberlite, is propelled to the surface of the earth by volcanic eruptions. Most of this diamond-bearing rock adheres to the walls of the volcano pipes.

2. Diamond-bearing rock that is propelled outside by the volcano is weathered by wind and rain and slowly disintegrates. The smaller fragments, diamonds and all, are washed from the mountain and end up in the immediate surroundings and in the riverbeds.

3. The river current washes the diamond-bearing rock down to the sea, where it is found in the river mouths and offshore.

It is assumed that the first diamonds were found in India, as early as 800 BC, and India remained the most important supplier of diamonds until the 18th century. Since circa 1650 Borneo has been a supplier to the Dutch diamond industry. Diamonds were discovered in Brazil in 1725, in Russia in 1829, in Australia in 1851, in South Africa in 1866 and in East Siberia in 1948. Today, diamonds are found in more than 20 countries — only Europe and Antarctica produce none. Of the total world production, around 5% is used for jewellery; the rest goes to industrial applications. Jewellery diamonds are cut in only a limited number of locations.

Diamonds and industry

About 5% of the total world production of diamonds is processed into jewellery diamonds: the rest is used for industrial purposes. Since the industrial revolution in the 19th century, diamonds — on account of their hardness — have had many applications: polishing discs, drills, chisels, but also in electronic appliances for drawing extremely thin and precise conducting wire, or in very precise medical instruments. In some industrial applications, diamonds are used up and have to be replaced regularly. So there is an ongoing demand. Since the fifties of the last century, it has been possible to produce artificial diamonds. Nowadays 95 to 99% of diamonds used in industry are synthetic.

Hardness: the Mohs scale

In 1822 the Austrian mineralogist Friedrich Mohs compiled a hardness scale for minerals, in ten stages running from soft (talcum) to extremely hard (diamond).

Objects in this gallery

• Coal / Carbon  Coal, like diamond, is made of carbon. (Collection: Brus.)

• Model of the diamond molecule  The diamond molecule is made up of 18 carbon atoms in an elementary cubic grid. Each carbon atom is tetragonally surrounded by 4 other carbon atoms. The distance between them is relatively small and the bonds are very strong. That explains the extreme hardness of the diamond.

• Model of the graphite molecule  Graphite, like diamond, is composed of carbon atoms and is highly regular in structure — yet graphite is soft and diamond is extremely hard. The difference lies in the way the atoms are bonded together.