Gigantic as the Cullinan diamond is, it represents only about half the daily output of the De Beers mines. By the end of 1904 ten tons of diamonds, valued at £60,000,000 sterling, had been removed from the Kimberley mines. It is difficult to imagine what has become of them all, and since they are, unlike paste, durable and permanent, how the demand for additions to those in use, keeps up. Twelve years ago about four million pounds was spent annually by the public on the purchase of diamonds. It is stated that the annual demand and expenditure are now even larger.
Diamond is a peculiar form or variety of the chemical element carbon--a very peculiar form most people will say who remember that charcoal and lamp-black are the common form of carbon. That one and the same unchangeable chemical element can exist as an amorphous black lump or powder, and also without addition or loss of chemical constituents, as the clearest, hardest, and most brilliant of crystals, is a paradox. The same strange capacity for existing in two totally different forms is exhibited by other fairly familiar elements. Sulphur is found in tertiary water-deposited clays in Sicily (it has nothing to do with Etna or Vesuvius) in the form of clear, lemon-coloured crystals half an inch or more in length. If you take some commercial stick-sulphur and melt it in a porcelain spoon, and pour half the melted stuff like treacle into a jar of water, you will find that it cools as translucent threads which are pliable and soft. The other half which you leave in the spoon to cool shoots out into the form of long brittle crystals of a needle-like shape. These two varieties of sulphur are nearly as different as lamp-black and diamond.
Diamonds are found at the Cape in a “blue ground” which is of volcanic origin, formed by the action of steam under enormous pressure. The blue volcanic mud has been thrust up from great depths in the earth’s surface in the form of “pipes” 100 yards to half a mile in diameter. It has long been known that at very high temperatures (4,000 deg. Centigrade) the metal iron dissolves carbon. The late Professor Moissan, of Paris, obtained artificial diamonds by suddenly cooling the iron in which carbon was dissolved by plunging the crucible into water. The outer shell of iron cools and forms a tightly closed shell enclosing the still liquid core. As this core cools it tends to expand, and thus produces an enormous pressure. The melted carbon cooling under this pressure assumes the crystalline colourless form known as diamond. There is good reason to believe that diamonds are formed, or have been formed, in association with metallic iron in a similar way, on a large scale, in great depths of the earth’s crust, and are shot up to the surface with other débris in the volcanic steam mud which is the “blue ground.”