Think About It Thursday: Where Do Diamonds Come From?


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Over the years it has been said that diamonds formed from the metamorphism of coal. According to, we now know this is untrue. “Coal has rarely played a role in the formation of diamonds. In fact, most diamonds that have been dated are much older than Earth’s first land plants – the source material of coal! That alone should be enough evidence to shut down the idea that Earth’s diamond deposits were formed from coal”.

There is thought to be 4 processes that lead to diamond formation. The first of the four processes is the most significant.

1. Earth’s Mantle- Geologist believe that diamonds form in the Earth’s mantle and are transported the the Earth’s surface by deep-source volcanic eruptions. The diamonds form from pure carbon in the mantle under extreme heat and pressure.

2. Subduction Zones- “Tiny diamonds have been found in rocks that are thought to have been subducted deep into the mantle by plate tectonic processes – then returned to the surface .”

3. Impact Sites – Throughout the Earth’s vast history, it has been hit by a large number of asteroids. These asteroids strike the Earth with intense heat and pressure that geologists believe that it is perfect for diamond formation. “This theory of diamond formation has been supported by the discovery of tiny diamonds around several asteroid impact sites.”

4. Formation in Space – “Smithsonian researchers also found large numbers of tiny diamonds when they were cutting a sample from the Allen Hills meteorite. These diamonds in meteorites are thought to have formed in space through high speed collisions similar to how diamonds form on Earth at impact sites”.

Coal is not a good source for diamond formation. Since coal is formed from plant debris and the oldest land plants are younger than almost every diamond that has ever been dated, it is easy to conclude that coal did not play a significant role in the formation of Earth’s diamonds.


Thanks for checking out this weeks Think About It Thursday! Stay tuned each week for more science related topics!

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