If one of these carbon crystals rises to the surface slowly, over decades or even years, the atoms binding its carbon molecules together return to their fail safe state, which is graphite – pencil lead. For carbon to remain a crystal, it must reach the surface in a burst, over no more than a few hours. To travel from the nursery to the surface, then, the stone must reach speeds of several hundred miles an hour. Such a speed can only be reached if the capping pressure is suddenly punctured through by a narrow fissure, at which point the temperature and pressure produces a massive volcanic explosion at the surface. For that to happen is unlikely. But over a billion years unlikely becomes inevitable.
The Cullinen was cut into nine large stones and 96 smaller diamonds, so many that it took 8 months just to polish them all. And if you ever get to the Tower of London, you might make a note that the Crown Jewels of England on display there, might be literally billions of years old, but they have only in the royal families’ possession for about a hundred years. But they will always be a testament to the creation of timeless beauty under pressure.
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