Rico's rants: Diamonds are forever

20 August 2014

Diamonds are forever

DelanceyPlace.com has a selection from Stuff Matters by Mark Miodownik:

Carbon is a light atom with six protons and usually six neutrons in its nucleus. In terms of all of its other properties and behavior, it is the six electrons that surround and shield the nucleus that are important. Two of these electrons are deeply embedded in an inner core near the nucleus and play no role in the atom's chemical life, its interaction with other elements. This leaves four electrons, which form its outermost layer, that are active. It is these four electrons that make the difference between the graphite of a pencil and the diamond of an engagement ring.
The simplest thing a carbon atom can do is share each of these four electrons with another carbon atom, forming four chemical bonds. This solves the problem of its active four electrons: each electron is partnered off with a corresponding electron, belonging to another carbon atom. The crystal structure produced is extremely rigid; it is a diamond.
The biggest diamond yet discovered is located in the Milky Way in the constellation of Serpens Cauda, where it is orbiting a pulsar star called PSR JI719-1438. It is an entire planet five times the size of Earth. Diamonds on Earth are minuscule by comparison. The biggest yet found is the size of a football (photo), extracted from the Cullinan mine in South Africa. It was eventually presented to King Edward VII in 1907 on his birthday and is now part of the crown jewels of the British monarchy. This diamond was formed far below the surface of the Earth at a depth of approximately three hundred kilometers, where, over the course of billions of years, the high temperatures and pressures converted a largish-sized carbon rock into the huge diamond. The diamond was then most likely carried to the surface of our planet during a volcanic eruption, where it lay inert and undisturbed for millions of years, until it was discovered a mile underground. The Cullinan in its rough state:

Each diamond is, in fact, a single crystal. In a typical diamond there are about a million billion billion atoms (1,000,000,000,000,000,000,000,000), perfectly arranged and assembled into a pyramidal structure. And it is this structure that accounts for its remarkable properties. In this formation, the electrons are locked into an extremely stable state, and this is what gives it its legendary strength. It is also transparent, but with an unusually high optical dispersion, which means that it splits light that enters it into its constituent colors, giving it its bright rainbow sparkle.
The combination of extreme hardness and optical luster makes diamonds almost flawless as gemstones. Because of their hardness, virtually nothing can scratch them, and so they keep their perfectly faceted shape and pristine sparkle not just throughout the lifetime of the wearer but throughout the lifetime of a civilization, through rain or shine, whether worn in a sandstorm, hacking through a jungle, or just doing the washing up. Even in antiquity diamond was known to be the hardest material in the world. The word diamond is derived from the Greek adamas, meaning 'unalterable' or 'unbreakable'.
Transporting the Cullinan diamond back to Britain posed an enormous security challenge for its owners, since the discovery of the largest ever rough diamond had been widely reported in the newspapers. Notorious criminals like Adam Worth, the inspiration for Sherlock Holmes' nemesis, Moriarty, who had already managed to steal a whole shipment of diamonds, were perceived to be a real threat. In the end, a plan worthy of Sherlock Holmes was hatched and executed. A decoy stone was dispatched on a steamboat under high security, while the real one was sent by post in a plain brown paper box. The ruse worked precisely because of another remarkable attribute of diamond: being composed solely of carbon, it is extremely light. The entire Cullinan diamond would have weighed little more than half a kilogram.