Diamonds and Coal
DO DIAMONDS REALLY COME FROM COAL?
Coal and diamonds share a common foundation, or base - the element carbon - represented by C in the periodic table. Carbon-based life forms, most commonly originating from plants, are transformed into coal by pressure. Carbon used to make coal is far from its purest form. Diamonds however, are made from a pure form of carbon that has been subjected to extreme pressure and heat in order for it to crystallize.
A terribly common misconception that’s persisted for decades is that diamonds are made from the metamorphism of coal. However, this theory is highly unlikely because most diamonds are so prehistoric, they actually date back millions of year. Therefore, most naturally-occurring diamonds are older than all plant life on Earth, which is the source material of coal.
WHAT IS THE REAL ORIGIN OF DIAMONDS?
It’s been established that coal was not even around prehistorically when nearly all the diamonds on Earth began their formation process. Interestingly, this “diamonds come from coal” myth is so widespread, it’s even taught in some classrooms today! While there may be a slight crossing over, coal has rarely played any role in the diamond creation process. Another difference between the formation of diamond verses the formation of coal, is that coal manifests as horizontal, or close to horizontal ,rock units composed of sedimentary rocks. In contrast, diamonds’ source rocks consist of pipes that are vertical and filled with igneous rocks.
WHAT ARE THE DIAMOND FORMATION PROCESSES?
Four processes exist that are thought to be responsible for all naturally-occurring diamonds on Earth. While three of these processes are considered insignificant, one process accounts for nearly 100 percent of natural diamonds. Regardless, coal is rarely involved in any of these four processes. Let’s take a deeper look at these processes.
MANTLE FORMATION OF DIAMONDS
All the commercial diamond deposits on Earth are believed to have formed within the mantle of the Earth’s crust, and brought to the surface by volcanic eruption. In order for natural diamonds to occur, the right conditions must be present, which includes extremely high temperatures and pressure. Therefore, diamond formation must occur approximately 90 miles below the surface where temperatures are at least a minimum of 2000 degrees Fahrenheit or 1050 degrees Celsius. Nearly 100 percent of natural diamonds are believed to have been formed by this process. Would coal be involved in this process? No. Because coal is rarely found more than two miles below the surface, it’s very unlikely.
SUBDUCTION ZONE DIAMOND FORMATION
Tectonic plates are thought to be responsible for the formation of tiny diamonds that have been found in rocks. These little diamonds were subducted deep in the mantle, then brought to the surface by plate movement. Is coal involved in this process? While coal is a possible source of carbon in this particular process, the oceanic plates are more likely for subduction than continental plates due to their higher density.
DIAMOND FORMATION AT IMPACT SITES
From the beginning of the Earth, asteroids have hit the surface repeatedly. During the impact, extreme pressures and temperatures are created which can lead to the formation of very little diamonds. In fact, tiny diamonds have been discovered at asteroid impact sites. Coal could potentially be present in the area of impact, however the carbon source could also be other carbon-bearing rocks such as limestones, dolomites, and marbles.
FORMATION IN SPACE
As discovered by NASA researchers, meteorites contain numerous nanodiamonds that are much too small to be used as gems or abrasives. Coal would certainly not be involved in this creation process that occurs outside of the Earth. Some diamonds may also be formed when a large asteroid strikes the earth, which is, fortunately for us, a rare event. Tiny industrial diamonds that have been mined in an impact crater in Siberia, Russia, as well as tiny diamonds found at craters in Arizona are thought to have been formed this way. Since they are formed at the surface of the earth, it is possible that coal could be involved in the diamonds’ formation.
