This tiny bubble of liquid carbon had been carried up in the slow subterranean river of molten lava. While the lava was cooling it solidified into an eight-faced crystal of geometrical symmetry the size of a green fig and so thoroughly had it been purged of impurity in the hellish furnace of the earth's core that it was transparent and clear as the suns own rays.
Rarer than gold, a diamond is the purest, most concentrated form of carbon and the hardest natural material on earth. Indeed, the word diamond comes from the Greek ‘adamas’, meaning 'invincible'.
Contained within the molten lava and rock 100 miles below the earth's surface are tiny bubbles of liquid carbon. Over millions of years the atoms in these carbon bubbles are purified by the intense heat, which is around 1300°C, and condensed by the massive pressure of the rock bearing down from above until they are packed tighter than any other substance.
Some of the bubbles are then carried up towards the surface in streams of lava that erupt along weak points in the earth's crust, carving out funnel-shaped pipes named kimberlite pipes after the first such formation discovered at Kimberley in South Africa. As the lava cools into a blueish rock called kimberlite, the carbon bubbles also cool and solidify into transparent symmetrical crystals, usually of eight faces and flawless.
Impurities that become trapped in the crystal give a diamond colour – a perfectly pure diamond is colourless, a blue diamond is tainted by boron, a yellow diamond by nitrogen, a green diamond results from radiation exposure, while rare pink and brown diamonds are thought to be the result of some defect in the diamond's molecular structure.
Diamonds were not originally purposed as jewellery but then, in the mid-15th century, it was discovered how to cut facets on a diamond's face so that they would reflect the light and show the full beauty of the stone. They rapidly became highly sought after.
The first known use of diamonds as jewellery occurred in 11th century Hungary when diamonds were used to decorate a queen's crown, and the tradition of a man proposing to his intended with a diamond ring began in 1477 when Archduke Maximilian of Austria gave Mary of Burgundy a diamond engagement ring.
The diamond finally became established as the most precious of gemstones with the discovery of some exceptionally large diamonds in South Africa and the opening of the world's first large-scale diamond mine at Kimberley in the middle of the 19th century.
Prospectors are usually alerted to the presence of a diamond bearing kimberlite pipe by the chance discovery of one or two diamonds in the surface soil, which will have been exposed by erosion. Termite mounds can also reveal the presence of diamonds below the surface.
Once the kimberlite pipe has been identified the rock is blasted and extracted from the ground and then crushed and milled – some 250 tons of earth must be mined to produce one one-carat diamond. The crushed rock is then wetted and passed across a table or belt smeared with grease. The wet gravel just rolls off while the diamonds, which repel water, stick to the grease. The diamonds are then measured and sorted for either cutting and sawing as gemstones, or for industrial use.
Today 80% of the world's diamonds go towards industrial uses. Because diamonds are so hard they make excellent abrasives and are used for cutting and polishing tools, in drill bits, grinding wheels, saw blades and as engraving tools. The other 20% of the world's diamonds are used for jewellery.