Are Diamonds Made of Coal?

Are Diamonds Made of Coal?

We’ve all heard the old adage that diamonds are made of a lump of coal, but we may not really know if the saying is actually true. Diamonds are formed in the earth, through a process that scientists, even today, don’t completely understand. This process is very similar to the process that creates coal, which is why people often believe the two substances are nearly the same. However, there are some important differences between the two.

Diamonds and Coal are Formed From Carbon

Carbon dioxide located about 100 miles beneath the surface of the earth is the source of diamonds. Coal is also formed from carbon, but is formed much closer to the earth’s surface, about two miles down. When coal is mined, miners go right to the source where the coal is formed. Diamonds, on the other hand, are brought close enough to the surface to be mined by volcanic eruptions.


In addition, the carbon that forms diamonds is much purer than that which forms coal. This is what creates a diamond’s clarity. Carbon that turns into coal usually includes other substances like hydrogen, oxygen, nitrogen, selenium and sulfur.

These impurities in coal are also why burning coal creates environmental problems like greenhouse gases. Some diamonds have minor impurities, as well, but these are far fewer than that in coal. Slight traces of nitrogen, for example, are what create the yellow diamond.

Diamonds Require More Heat and Pressure

Coal is formed from heat and pressure, just like diamonds. However, diamonds require much greater temperatures and far more direct pressure to form, which is a primary reason why the end result is so different. This extreme heat and pressure can only be found far into the earth. Since coal is formed near the surface, the heat and pressure are far less severe.

Diamonds require temperatures of about 2200 degrees Fahrenheit, and pressure of about 725,000 pounds per square inch.  It is this extreme heat and pressure, followed by cooling, which gives diamonds hardness not found in coal or any other substance.  The cooling takes place when the diamonds are forced to the surface by the volcanic eruption.

Coal is Formed Mostly From Plant Material

Like diamonds, coal was formed billions of years ago. However, unlike diamonds, coal’s carbon comes from many different substances, most notably, from decomposed plants. This is why the carbon that forms coal is not as pure as that which forms diamonds.

So, Diamonds Are Not Made of Coal, After All

Though there are definitely similarities, we can say conclusively that diamonds are not made of coal. Both substances and processes are unique and amazing in their own right. Both are somewhat mysterious, even to scientists who have studied these extensively. So, stop trying, because you’ll never turn your lump of coal into a diamond!

Diamonds, even before being cut and polished bear no resemblance to coal, even though the two have very similar origins. Color and hardness are two obvious differences, but there are others, as well.


Carl A. Jones, GIA GG

Carl A. Jones is a GIA Graduate Gemologist with over 20 years of experience in the diamond industry. He is an independent jewelry appraiser. He specializes in determining the value of diamonds and advising consumers on how to buy quality diamond jewelry.

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