In most cases, giant machines dig for the gems, which are separated from the gravel by weight and identified by a sophisticated x-ray system. Mines are created in regions with a high concentration of a type of rock, called kimberlite by geologists. This material is formed by the cooling of magma, which reached the surface millions of years ago, carrying elements from deep regions of the Earth. Made of carbon subjected to extremely high pressure, diamonds were forged up to 200 km below the surface at least 3 billion years ago.
The most common type of mine is the open pit – as represented in the infographic below –, based on the excavation of kimberlite, and most of them are in Africa. In Brazil, production is concentrated in mines formed by kimberlite erosion. The waters of rivers and groundwater carry stones, which are concentrated in surface areas and are exploited by miners. The 26 tons of diamond produced in the world move US$ 13 billion. The biggest buyer is China.
HARD WORK
Super machines, explosives and high technology are used to sift through tons of rock.
softening the earth
After finding geological evidence of the presence of diamonds, miners excavate the kimberlite. But their tool is not a pickaxe, no: the guys place explosives in holes up to 17 m deep made by the drilling machine. The objective is to turn the hard rock into gravel.
hard stop trio
Three giant machines do the heavy lifting: the drill opens holes in the rock for placing explosives, the excavator moves up to 50 tons of rock per minute and the mining truck takes 100 tons of material for processing.
Deep hole
As the excavation progresses, the well becomes more funneled, reaching hundreds of meters deep and kilometers wide. The largest diamond mine in operation, 600 m deep and 1.6 km in diameter at its widest part, is Argyle Diamond, in Australia.
Plan B
When the excavation tapers too much, a tunnel must be dug parallel to the pit. From the main tunnel, perpendicular tunnels depart to extract the deepest rock. Underground, smaller versions of the machines employed aboveground are used.
thin thing
The material extracted from the mine goes to processing. The gravel is crushed twice, washed and sieved. Then, the pebbles – from 1.5 to 15 mm – go to a flotation tank. The heaviest stones, with the potential to be diamonds, remain at the bottom and the lightest are discarded.
picking corn
A sorting machine equipped with X-rays identifies the diamonds. As they roll on the treadmill and are hit by radiation, they fluoresce. A sensor registers this light and triggers a jet of air, which separates what matters from the rest of the stones. Finally, there is a manual check.
made to shine
About 30% of diamonds are gemstones, that is, they have the ideal characteristics to become jewelry: color, clarity, size and possibility of cutting. The remainder is used in industry to produce cutting parts, such as drills, discs, saws and scalpels. As they transmit heat quickly, diamonds are also used in precision thermometers.
IT’S WORTH AS MUCH AS IT WEIGHT
Each ton of earth extracted yields 1 carat of diamonds (0.2 g)
Market value
A loaded truck yields up to 20 1g diamonds. Stones used in jewelry are worth, on average, $1,000/carat. For industrial use, you pay around US$ 10/carat.
beyond the glow
Diamond value is based on color, clarity, size and cut. Blue, orange, red and pink gems are rare. White and yellowish are more common (98% of the total).
crown jewel
The largest of the diamonds was mined in South Africa in 1905. The rough stone weighed 3,100 carats and was cut in nine. The two largest (Cullinan I and II) were given to British royalty.
– In 1714, the first diamond was found in Brazil, in a gold mine near Diamantina, MG.
– The most expensive diamond in the world was auctioned in London for $46 million. Graf Pink weighs 24.78 carats and is pink in color.
CONSULTANCY Geraldo Norberto Chaves Sgarbi, from the Geology Department of the Geosciences Institute of the UFMG University, and Renato Santos, president of Brasil Comércio de Diamantes SOURCES Book Macroscopic Petrography of Igneous, Sedimentary and Metamorphic Rocks, by Editora UFMG; Rio Tinto’s Diamantes newsletter; websites debeersgroup.com, riotinto.com,diamonds.cn, fundep.ufmg.br, visualcapitalist.com; and documentaries Superconstructions: Diamond Mines, from Discovery Channel, and Extraordinary Machines: Mining Truck, from National Geographic
Read too:
– How are diamonds cut?
– What is the hardest material that exists?
– What is the largest gemstone ever found?