Diamonds, eyes of a basilisk, fascinate all who see them. People die and kill for them. Yet diamonds are just a form of carbon, the substance on which all life is based. The life cycle of a diamond takes millions of years to go from carbon to diamond to graphite. Here is a tiny fraction of the story.

A diamond is made from carbon that is subjected to the  right combination of pressure and temperature. This can happen either in the earth or  in a special vessel. Natural diamonds form as a result of carbon in the earth's mantle being pushed deeper into the  Earth's crust where it melts and becomes new rock  if it cools. Depending on temperature and pressure the carbon may remain as rock, become graphite ( used for pencil leads) or diamond. Diamond formation requires high pressure and relatively low temperature. Diamond is a metastable state of carbon and   may  melt or revert to carbon. Diamonds may also be formed as a result of the high pressures encountered in a meteorite strike and some diamonds, known as carbonado diamonds  may have been created  extra-terrestrially and carried here by an asteroid.

Diamonds are carried to the surface by volcanic eruptions where the  magma originates at depths greater than about 100 miles, which is much greater than the depth at which most magma originates.  and  is relatively rare. These small scale eruptions result in narrow pipes of diamond bearing material from  short lived dead volcanoes.  Diamonds are also found in metamorphic rocks, when  the pressure becomes high enough to create diamond from carbon.

All diamonds at or near the surface of the earth are slowly turning into Graphite,  Buy now while stocks last

Natural Diamonds are therefore rare,  and,  according to [2]  100 tons of mud produce one carat (200 mg) of diamonds, not necessarily as a single stone.  Only a quarter of the diamonds mined are made into jewellery and not all of that is of high quality. Occasionally a diamond  will come out of the earth without needing polishing, but such diamonds, known as “glassies”  are rare. Rodney Cox, in a note in the Borealis Technology  newsletter also claimed, some years ago that diamonds are common on parts of the sea bed.  However you look at it gem quality diamonds are rare, and even industrial diamonds are not that common.

On the microscopic level a diamond  is a crystal where  the atoms are arranged  in an octahedral lattice with electrons shared between adjacent carbon atoms. (this is called covalent bonding) Whereas graphite, the most stable form of carbon arranges itself into thin sheets which  can be easily separated, diamond is equally strong in all directions. As a result diamonds are just about the  hardest naturally  occurring substance with a hardness of  10 on the internationally recognised standard, the Mohs scale, thought recent theoretical work indicates some substances, presumably not known to occur naturally may be much harder.

While hard,  diamond is relatively brittle, and more brittle if struck in certain directions, known as cleavage planes, This allows  cutters to  turn a single large gem into  several smaller gems using chisels as would a sculptor. Cutting a diamond this way requires  great skill and experience. I read that the cutter who got the job of cutting and polishing the Cullinan,  one of the largest diamonds ever found,  studied it for a year or two before deciding to cut and fainted after making the first tap.

The diamonds generally considered the best are  colourless, transparent and free from inclusions (The number and type of inclusions can be used to distinguish between natural and synthetic gems). The lack of colour arises because, in the absence of impurities it absorbs  no light and reflects almost none ( if it transmitted all light you would not be able to see it). Impurities  colour the diamond usually by replacing carbon atoms in the lattice.  Most commonly Nitrogen will  colour the diamond yellow or brown and the standard diamond grading scale takes account of this. Boron will produce a blue diamond  crystal irregularities make it pink and natural radiation can  produce a green diamond.

Top quality fancies, as such diamonds are called, are subject to a different grading scale and  are often worth more than a colourless diamond of the same weight and clarity.  Examples include canary yellow, blue, green, and red diamonds.

In a later article I want to look at how to avoid being cheated when buying a diamond. The safest thing is to buy from a reputable dealer who will give a certificate. Otherwise anything can happen. My grandfather told a story where he was walking in Moscow, early in the 20th century and heard two Russians talking about how they had to sell a bag of diamonds urgently. Being only a teenager but having some money he instantly grabbed the bargain only to find the “Diamonds” were glass. This he regarded as an educational experience. In the Philippines a few years ago fake diamonds were referred to as”Russian Diamonds”.

By one of those coincidences of fate that make good stories the only time I purchased a diamond was from a Diamond factory in Amsterdam recommended by a Chinese waiter in a Thai Restaurant.

Diamonds part two artificial and fake

This is only a partial list.  It is a vast field

[1] how diamonds are formed

[2] Wikipedia

[3] Why diamonds are hard