The most common explanation for diamond formation is that coal (plant fossils) was compressed into the ground and became diamonds when it became hard and transparent.
That's what the elementary school teacher told us, but it wasn't true. The environment in which the diamond is formed is much more extreme.
In the year that Super Diamond was born, Hollywood launched a boring movie called "Rescue in the Heart of the Earth", which is a science fiction film that looks quite real.
There was one scene that impressed me. Several scientists were launched into the mantle and hit the core with nuclear weapons. In the process, they had to dodge diamonds as massive as tall buildings.
A real diamond can't be that big, but it's in the right place. Diamonds are indeed formed in the mantle, not in the earth's crust.
Diamonds contain only carbon, and it takes billions of years to form a diamond.
Plants do contain carbon, but it takes a long time to turn from fossil plants to diamonds, and the diamonds we dig up from mines today will not be compressed from plants. To compress carbon into crystals, it also requires very high pressures and temperatures, which are not possible in the planetary crust.
Diamonds are formed hundreds of kilometers deep from the upper mantle, where pressures are hundreds of thousands of times higher than atmospheric pressures and temperatures comparable to the surface of the Sun. After the diamond is formed, it will reach the surface with the volcanic eruption, and eventually we will dig it out.
Rumors of plant compression may have emerged because we also mine coal, which is formed by heating and compressing plant fossils. But because the temperature and pressure are far from enough, it is not enough to form a diamond.
Coal and diamonds can indeed be converted, but contrary to rumors. Diamonds are not stable and decay into coal over time. So we want to know, can this process be reversed?
In 2003, Tetsuo Inuchi, a researcher at Tokyo Institute of Technology, began experimenting with compressing coal into diamonds. The equipment used by Tetsuo Izumi was equivalent to a large pressure cooker, and he threw a large pile of coal into it, setting the pressure higher than in the mantle. The result is a super diamond that no one has seen before.
Ultra diamonds have a Hardness of more than 10 on the Mohs scale, but no one has yet calculated an exact value. The coal is greatly compressed, and the resulting super diamond is only a tiny bit, about a few millionths of a gram.
However, coal is not an indispensable material. Dan Frost of the Bavarian Geological Institute in Germany succeeded in compressing peanut butter into diamonds. Headquartered in Illinois, Treasures of Life is able to crush the ashes of your deceased loved ones into diamonds. As long as there is carbon, it can become a diamond.
Coal, diamonds, and hyperdiamonds are all made up of the same element, but they have different properties (we call them "allotropes of carbon"). This indicates that the elements can be arranged in different structures.
Source: Tim James, How the Periodic Table Explains Everything, Chapter 2