Diamonds are just carbon, rather pure, common if found in form of coal or graphite, but extremely valuable in form of a diamond. Diamonds are different, because they consist of carbon in a very special and rare crystal grid, where the characteristics of the mineral change. It becomes a translucent crystal, the hardest rock on Earth and valuable for industrial and jewelry purposes.
The conditions to produce a diamond from plain carbon were discovered many decades ago: high pressure and high temperature, but no oxygen. Today it is possible to produce artificial diamonds by using the same environment which produced them in nature. But where did those strange conditions exist in nature? The answer are volcanic tubes called pipes deep inside earth. Those pipes, filled with lava which tried to emerge to the surface, have a high pressure because of the deepth and a high temperature because of the lava. If there is also carbon, diamonds are formed.
Those conditions are very rare, and so only very few deposits of diamonds exist worldwide. Most of them are concentrated to a rather small area, located in south-western Africa and eastern South America. Originally a single connected area, when the supercontinent Gonwanaland was still in one piece, 200 Mio years ago, they are now on two different continents.
The first discovery of of such a diamond pipe was made in Kimberley in South Afrika. The typical rock of the pipe was called Kimberlite after this location.
The diamond mining started with several rushes around 1866, when the first diamonds were discovered near the Orange River. The first diamond found there ever is said to be the Eureka with 21.25 carat. The first years are comparable to other rushes, like the gold rush in Alaska. But soon the mining company were founded and after some decades only De Beers remained. Today it seems, diamonds are the monopoly of one single company which controlls virtually all diamonds on Earth.
Such a situation is always good to produce jealousy in the competitors, but also despotism and exorbitant prices by the monopolist. A common accusation against De Beers is the way the company treats its workers. Of course, they have many cotrolls to make sure no worker steals a diamond. The workers mine valuables worth a whole life's work, and get only a few pennies. We can not judge the situation of the workers, but the number of critical publications about working conditions at De Beers mines is overwhelming. So we guess a little caution is advisable when visiting one of their mines.