Diamonds consist of pure carbon that crystallized under very high pressure (up to 70,000 kg/cm²) and temperature (up to 2000 C). Such an environment exists only at depths of 150 to 200 kilometers. Diamonds make their long journey to the surface of the earth by intrusions of the volcanic stone in which they are found, kimberlite or lamproite. Kimberlite or blue ground is called after the South African city Kimberley.
Many volcanos have eroded away in the course of the centuries thus causing the diamonds to be released from the kimberlite. They are then washed away and carried to river beds and even further, to the places where they are ultimately found. Other volcanos still have kimberlite pipes, which are mined.
Diamond is the hardest mineral known to man (its hardness coefficient is 10 on the Mohs scale). Thanks to this hardness, the diamond could make its journey out of the crust of the earth. It is estimated that the kimberlite found in Africa and South America was created between 70 and 150 million years ago at the time of the great rending of the earth's crust that drove the continents apart.
Until the 18th century, the India of the vastly wealthy maharajas was the only supplier of diamonds in the world. Since the second half of the 19th century this has changed. Africa became the largest producer with the most important suppliers, being Zaire for industrial diamonds and South Africa for gem quality diamonds. Since the beginning of the eighties, Australia takes the lion's share of the diamond production. Also Botswana and the ex-Soviet Union become very serious partners on the world market, while South Africa, Namibia, Angola, South America, Central African Republic, Ghana, Sierra Leone, Liberia, Tanzania also substantial producers are.
The methods of mining diamonds are very diverse depending on the way in which the diamonds are present on the earth's surface. The mining of pipes of dead volcanos is done by open-pit mining or by digging underground mine shafts. In both cases, the kimberlite blocks obtained by breaking up, dynamiting, or digging are trucked to the processing plant where they are crushed and washed until a concentrated diamond-containing residue is obtained.
Where the diamond crystals are freed from the kimberlite matrix by erosion and are carried along by rivers, the mining can be done more directly. The exploitation of sandy coastal strata generally is done by open terrace construction where the diamonds are sought both by hand and by refined techniques. In the river beds, the diamonds are "harvested" by sorting and washing the dug, pumped, or dredged river gravel (alluvial mining). The finding of diamonds can thus be the result of large industrial operations, artisanal methods, and even manual labor.
Diamonds are rare. 250 tons of rock, sand, and gravel must be physically moved to yield 1 carat of diamonds (= 1/5 of a gram).
The annual world production amounts to approximately 100 million carats of which only 50% are of gem quality.
The exceptional value of diamonds as gems needs no demonstration. But their industrial application too has long been known. Already in antiquity, diamonds were used for engraving glass and the polishing of other gems. Because of their hardness, diamonds are now being used in many industrial sectors. Thus, for example, diamonds are used in the production of optic objective lenses and contact lenses and in the manufacturing of precision parts and extremely fine threads where an accuracy of a few microns is required. Naturally, diamonds are the ultimate material for polishers, drill bores, trepanning and percussion bores. Thus, diamonds are used in soil research, in the drilling of reinforcing bars on runways, in the grinding down of highways, to name but a few applications. There are also applications in which diamonds are used for their clarity and optic qualities as in the Space Shuttle.
Another aspect of industrial diamonds is their synthetic production. Diamonds are merely carbon, but then with a very specific atom structure, which can only be obtained under very special conditions of pressure and heat. Presently, many synthetic diamonds are manufactured for industrial applications because natural diamonds can no longer satisfy the demand. Since 1970, it has even been possible to manufacture gem quality diamonds synthetically, but the cost is too high to make production profitable even in the future.
