How are diamonds made out of coal?

Diamonds are forever; at least according to James Bond. Of all the precious stones out there, from rubies to emeralds, people have some special affinity towards diamonds, which is also the hardest natural substance on Earth. And this interest surely reflects in its price.
A popular myth that has found its way around is that diamonds are made out of coal. The belief is so ingrained that it led to the birth of quotes like this: “A diamond is just a piece of charcoal that handled stress exceptionally well.” While the precious gem and the coal are not much different from each other, there is very slim chance that the former is born from the latter. Interestingly, the primary component of both materials is the same element: Carbon.
The myth that diamonds are formed from coal can be debunked from the simple fact that the former is way older than the latter. The origin of all the diamonds excavated so far traces back to before the Cambrian period, about 550 million years ago. The age of these diamonds is estimated to be between 1 billion and 3 billion years.
Diamonds are minerals surrounded by igneous rocks. Unlike the other gems, they are formed solely by carbon. The formation of diamonds requires immense pressure and ultra-high temperature. They are formed between 90 and 120 miles below the Earth’s surface where temperature is around 1000 degree Celsius. Since they are formed so far below, you may wonder how we could find them. They are brought to the surface by phenomenon known as deep source volcanic eruptions. It is such a rare occurrence, and hasn’t happened since it was recognized. Diamond is one of the two pure forms of carbon, the other being graphite. The carbon source of these diamonds is believed to be the carbon that was trapped in the planet’s interior at the time of its formation
Coal on the other hand is a fossil fuel, found no deeper than 2 miles below the surface. It is formed under high pressure as well, but from the fossils of living organisms. And the coal seams are sedimentary rocks while diamond blocks are, as mentioned earlier, igneous rocks. The sources of coal are the sediments of plants, and the earliest plants on Earth didn’t appear until 450 million years ago.
Other than deep source eruptions, the two other processes how diamond may be formed are subduction of tectonic plates and asteroid impacts. However, these processes also rarely involve coal. Coal could be present in the sites where they could happen, but the possibility is very low.

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