How Are Diamonds Formed?

From engagement rings to fine jewelry, diamonds are so common in our everyday lives that it’s not often that we stop to think about where they came from. But the journey that these little gems make, from formation to the jewelry store, is really quite impressive. How is a natural diamond formed? Where are diamonds found? What are diamonds made of? This precious stone poses numerous questions.

Several loose diamonds In this article, we’ll explore the main ways diamonds are formed and where diamonds are found. From deep beneath the earth’s surface to a well-regulated lab, you might be surprised by where these dazzling stones are found.

Are Diamonds Made From Coal?

Contrary to what you might have learned in science class, diamonds are not made from coal. The old wives’ tale that diamonds were once pieces of coal that have evolved after years under high pressure and temperature is nothing more than a common myth. In fact, diamonds are actually much older than the earth’s plant material, the main ingredient for coal creation.

A rough diamond An additional flaw in this theory is that coal seams are sedimentary rocks that often occur in horizontal layers. So what are diamonds made of? The source rocks of diamonds are found in vertical layers combined with igneous rocks. A natural diamond is made of carbon when carbon atoms bond together under pressure and form the crystals you see in diamonds.

How Are Diamonds Formed?

Simply put, diamond formation occurs when carbon deposits deep within the earth(approximately 90 to 125 miles below the surface) are subject to high temperature and pressure. Some stones take shape in a matter of days or months, while others take millions of years to materialize. In the case of colored diamonds, the color is caused by trace elements interacting during the diamond’s formation. Additionally, it’s almost impossible to determine a diamond’s exact age, but inclusions of specific minerals help geologists to form an estimate.

That being said, most natural diamonds date back millions, if not billions of years. And, interestingly enough, diamond growth isn’t always an uninterrupted process. A rough diamond’s formation can be disturbed due to a change in temperature or pressure. The gemstone could then wait for hundreds or even millions of years for conditions to be suitable for growth to continue.

Methods of Diamond Formation

There are four main processes that are believed to be responsible for nearly all diamond deposit sites found near the earth’s surface – diamond formation in the earth’s mantle, diamond formation in a subduction zone, diamond formation at impact sites, and diamond formation in space.

Diamond Formation in the Earth’s Mantle

Geologists believe that nearly 100% of the diamonds found in diamond mines, and thus used in engagement rings, were formed in the upper mantle and delivered to the earth’s surface by a deep-source volcanic eruption. These volcanic eruptions are credited with creating the kimberlite and lamproite pipes that gemstones are found in. explains these kimberlite pipes and their relation to diamond mining as the following, “Most of these pipes do not contain diamond, or contain such a small amount of diamond that they are not of commercial interest. However, open-pit and underground mines are developed in these pipes when they contain adequate diamonds for profitable mining. Diamonds have also been weathered and eroded from some of these pipes.”

Diamond Formation in Subduction Zones

This second method of diamond formation occurs when rocks are pushed into what geologists call “subduction zones” by tectonic plates and then return to the surface with tiny diamonds. Interestingly, the small rough diamonds formed in subduction zones grow just 50 miles below the earth’s crust at temperatures as low as 390 degrees Fahrenheit(yes, that’s low compared to the usual 2,000 degrees).

A diamond mine Rocks that have journeyed to subduction zones and back are super rare. No known commercial diamonds have been found within them as they are very small and not sold by jewelers. However, an interesting discovery was made as some stones uncovered from subduction zones are believed to contain traces of oceanic crust, appearing as blue diamonds.

Diamond Formation at Impact Sites

Throughout its history, Earth has been subjected to a hit or two from a few asteroids(just ask the dinosaurs). When an asteroid collides with the earth, it produces intense pressure and temperatures, two qualities that are perfect for creating diamonds. This process can be viewed at several asteroid impact sites around the globe, two of the most popular of which are the Popigai Crater in Siberia, Russia and, the Meteor Crater in Arizona.

Diamond Formation in Space

Little green men aren’t the only things floating around in space. NASA researchers have found large amounts of nanodiamonds in some meteorites. Unfortunately, these diamonds are far too small to use for diamond jewelry or industrial abrasives, but they still make for a fun discovery.

Image of the night sky What’s more, the Smithsonian found large amounts of tiny diamonds in the Allen Hills meteorite, providing more evidence that space diamonds are indeed a thing.

Lab Grown Diamonds

A mined diamond has been sought after since the beginning of diamond jewelry but the past few decades have made way for a comparative alternative. By the 1950s, scientists harnessed the intense heat and pressure required to create synthetic diamonds in a lab. The earliest of these lab created stones were not gem-quality. However, as technology evolved, engineers manufactured a perfect, pure carbon lab grown diamond.

Lab diamonds undergo a technique referred to as “HPHT,” an acronym that stands for high pressure, high temperature. HPHT was designed to mimic the process that natural diamonds undergo within the earth. First, a small diamond seed is placed with a carbon seed – such as graphite or diamond powder – where it is then exposed to extreme heat and pressure. As the pure carbon melts a diamond forms around the diamond seed. Next, the new substance is left to cool before it’s ready to be cut, polished, and set into its final form.

Jewelry featuring lab grown diamonds We believe the debate is settled because whether created in a lab or by the earth’s crust, neither process affects the diamond quality. Why buy lab grown diamonds? A Lab grown diamond is a great choice if you are looking for ethical engagement ring options. Unlike mined diamonds, which take millions or even billions of years to form, lab grown diamonds materialize within a matter of weeks. Mined diamonds are not typically a sustainable engagement ring option. And just like mined diamonds, you can customize their shape by choosing one of many different types of engagement ring cuts.

Another method to create man made diamonds is chemical vapor deposition, also known as CVD. Just like HPHT diamonds, CVD diamonds are also real, gem-quality diamonds. The Gemological Institute of America(GIA) explains it as such, “(CVD)involves introducing a gas, such as methane, into a vacuum chamber, then activating and breaking down the molecules of the gas with microwaves. This causes the carbon atoms to accumulate on a substrate, similar to the way snowflakes accumulate in a snowfall.“

At 12FIFTEEN, we offer lab grown diamonds as mined diamond alternatives. A lab diamond is generally more affordable and attainable than a mined diamond. A lab created diamond also doesn’t come with the unethical works of diamond mining.


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