Throughout many science classrooms, the “how diamonds form” story is based on the metamorphism of coal.
It is doubtful that coal has ever played a part in diamond formation. In fact, the majority of diamonds that have been dated are much older than the first land plants – the source material of coal! That is enough evidence to negate the theory that diamond deposits are formed by coal.
It is also important to point out that coal seams are sedimentary rocks, meaning that they are usually found as horizontal or nearly horizontal units. However, the rocks from which diamonds are formed are vertical pipes full of igneous rock.
Diamonds are formed underground at high pressures and temperatures, making them similar to coal. Despite this slight similarity in origin, diamonds are nothing like coal at all.
It is important to note that coal forms much closer to the ground than diamonds, which makes sense when considering that coal contains some plant matter from the Earth’s surface.
As well as that diamonds are pure phases or polymorphs of carbon. They are pure carbon minerals subjected to high temperatures and pressures. On the other hand, coal is a mixture of plant matter and carbon.
A diamond requires not only pressure to form but also enormous amounts of heat. In fact, diamonds require a combination of heat (thousands of degrees) and pressure (130,000 atmospheres), both of which can typically only be found about 90 to 100 miles beneath the surface of the Earth, deep within the mantle.
During this process, heat and pressure combine to form the crystal lattice structure we are familiar with. In a tetrahedral unit, carbon atoms bond with four other atoms when exposed to heat and pressure. As well as providing diamonds with their classic hardness, this molecular bond also provides their structure. Impurities on any level other than superficial could not form that bond.
How does a diamond end up on our fingers if it is formed so far below the surface? The process began millions of years ago when volcanic eruptions brought the diamonds closer to the surface. Their original eruption sites were dispersed further by erosion, geological shifts, streams, and other processes.
Some diamonds are derived from slightly different sources. Deep-sea oceanic tectonics may have created some, while asteroid strikes may have produced others.
It’s a fact that diamonds aren’t like coal that did well under pressure. Your friends might not think you’re a lot of fun at parties, but they won’t be able to say you don’t know your stuff about diamonds.