The diamond is a natural mineral composed mostly of carbon (99.95%). The diamond’s crystal structure belongs to the cubic system. The diamond is usually an octahedron and less often has the shape of a cube or a dodecahedron. The following conditions are needed to transform carbon into a diamond crystal: a pressure of 100,000 bars and a temperature of about 2,500ºC. Ambient conditions of this type only occur at depths of 130-200 kilometres below the surface of the earth in active volcanoes. Diamonds melting point is 3,700ºC, its specific gravity is 3.52, its hardness is 10 and its refractive index is 2.417.
Diamond’s Crystallizations – Theories:
The first diamonds were found in ancient and present riverbeds, but towards the end of the 19th century, diamonds were also found in large volcanic pipes, which had penetrated into the depth of the earth. Diamonds are in fact found in volcanic tuff rock called “kimberlite” that had been primarily considered either hardened lava or the basic material of extinct volcanoes.
Later this assumption has been refuted. The kimberlite rock has many large spaces thick with kimberlite. Kimberlite is not the parent rock of diamonds it is rather the host rock. The question of diamond formation was still open.
In the first part of the 20th century it was a common belief that diamonds were formed in the eclogite rock of the kimberlite pipes. The truth is that sometimes diamonds are found in the eclogite rock but they are never formed there.
Even the most recent theories about the diamond’s formation process are not conclusive; although it is certain that diamonds have been created in the earth depth, deeper than any other gemstones.
The connection between kimberlite pipes and diamonds is still unknown.
It is possible that fluids enriched with carbon monoxide, nickel, iron and copper are very important components in diamonds formation, but the formation process is still unknown. Some claim that graphite becomes a diamond as in the production process of synthetic diamonds. Others claim that carbonic fluid or gases are at the origin of diamond formation.
Other theory says that diamond “seeds” have been created in the earth crust and “grew” with the addition of carbon atoms to the “seed”. The external layers are formed by carbon dioxide or the oxidization of methane; these gases also cause the move of kimberlite rock to the surface.
The kimberlite rock (the host rock) is not lava, because lava erupts at 1,000/1,200ºC and at this temperature diamonds would melt.
Another theory claims that methane and not carbon dioxide is the basic material of diamond. This gas is the simplest source of carbon; it can be separated from the magma in high temperatures and high-pressures conditions and after cooling of the magma’s the pressure could create appropriate conditions for diamonds formation.
It seems that diamonds were created, during a long period of time, from carbon, in liquid magma pools in the earth crust. Apparently some other minerals were created in the same magma that was probably in a plastic state and had been moved upward by gas explosions in the depth of the earth. On its way to the surface this magma punctured the earth crust with a relatively small number of pipes, which eventually cooled and hardened. The magma on its way upwards underwent a chemical transformation and a number of rocks and minerals were added, thus the kimberlite rock was created.
In this powerful process many minerals were released, some were broken; some altered their form etc. Even though many people refer to the kimberlite pipes as the original source of diamonds, this is not correct because diamonds were transferred to these pipes from the earth depths.