Carbon as an element often gets a bad name; what with all this carbon monoxide and carbon dioxide which leads to global warming. We can often forget about what our favourite form of carbon is, a girl’s best friend – Diamonds. Diamonds are the hardest naturally occurring material on earth, they cannot be burnt by fire and can only be scratched or cut with another diamond. If that isn’t badass enough, the name Diamond itself comes from the greek ἀδάμας – adámas “unbreakable, however the word contains reference to the word δαμάω (damáō), which means “I overpower”or “I tame”.
Whilst diamonds are not the most stable form of pure molecular carbon (Graphite is) they do have different crystalline forms – this is called polymorphism. A few of the more recent discoveries and interesting ones involve Lonsdaleite which forms when a meteor containing graphite hits earth, now that’s a pretty rare rock for your ring.
However the toughest naturally occurring form of diamond is the Carbonado – or black diamond. The origins of the formation of this curious crystal are not known and are somewhat controversial. They formed 3 billion years ago and can only be found in Brazil and the Central African Republic, theories include shock metamorphism whereby a meteor strikes earth creating enough heat and pressure to force atomic carbon to pack together in the strongest and most efficient way, forming a diamond. Another theory is radiation-induced diamond formation which is when the spontaneous fission of the isotopes of Uranium and thorium cause enough energy to form diamonds.
“The toughest naturally occurring form of diamond is the Carbonado – or black diamond”
So how exactly are diamonds made? Natural diamonds are made when heavily carbon based materials are subjected to extremely high pressure, around 4500000000-6000000000 Pascals (GigaPascals) and around 1500 degrees kelvin. These conditions occur below the Earth’s surface in the lithospheric mantle, and generally below continental plates.
Superman can famously make diamonds just by squeezing a lump of coal, unfortunately for Clark Kent, but fortunately for the diamond jewellers, this is not actually possible, coal has many impurities in it such as sulphur, hydrogen and mercury, so it is not possible to turn coal into diamonds by subjecting it to high pressure. However there is a lot of research going into synthetic diamonds, not only into those which can be of gem grade quality, where the money is, but also into industrial grade diamonds which can be used for drill bits, polishing and thermal conductors.
“Natural diamonds are made when heavily carbon based materials are subjected to extremely high pressure”
In scientific labs the most common synthesised diamonds are made via HPHT (high-pressure high-temperature) and CVD (chemical vapour deposition). The latter is quite a successful method of making diamonds, it works by creating the necessary circumstances for carbon atoms in a gas to settle on a substrate in crystalline form. Unlike natural diamonds CVD diamonds occur at low pressures (atmospheric) and can be made from filament lamp heat sources as well as microwaves, so long as enough heat can be generated to create a plasma type state.
There is a remarkable step by step guide on how to make a ‘diamond’ using some cotton string, olive oil, graphite and a microwave. The man seems to suggest if you soak a very small section of your string In olive oil, tie it gently around your length of graphite and allow the oil to soak in and then proceed to microwave your graphite on full power for about an hour and a half in a ‘crucible’ then voila – you have made a diamond! However I doubt your landlord would be thrilled if your microwave broke, the man did warn of sparks.