How Do Diamonds Really Form? (Not From Coal!)

Trevor English

Diamonds top the list on the Mohs hardness scale and are some of the most valuable gems on the planet – neglecting that De Beers Diamond Cartel controls the price. Other than for pleasant gifts to your significant other, these stones are significantly useful in various industries. So, how are they made? Hint: it isn't from coal.

How they form

On its own, carbon cannot form diamonds under the surface of the Earth. In order to form, subsurface carbon, about 100 miles (160 km) under the surface of the Earth needs to be subjected to immense heat and pressure. Both coal and diamond are made primarily from carbon, but their chemical structures are significantly different.

Coal is formed from highly impure carbon that often contains elements like oxygen, selenium, hydrogen, nitrogen and sulfur. Diamond, on the other hand, require a very pure source of carbon, any defect in purity can cause the diamond to change color or become undesirable.

When near-pure carbon sources like carbon dioxide are trapped deep under the Earth's surface, conditions are almost set for diamonds to form. About 725,000 PSI (5,000 MPa) is needed to press the carbon into a strong diamond lattice that has a 3-fold symmetry. Temperatures also need to reach about 2,200˚F (1204˚C).

How Do Diamonds Really Form? (Not From Coal!)

[Image Source: Pixabay]

Diamonds begin to form when these conditions are met. The carbon atoms begin to bond with four other carbon atoms, which creates the proper lattice and is the source of diamond's strength. Once the diamond is created, the next step is traveling from the depths of the Earth all the way to the surface to be mined and found.

How they move to the surface

Most diamonds that are found today were brought to the surface through volcanic eruptions, often violent in nature. Scientists believe that the process of moving them from their formation location to the surface would have occurred in a couple of hours. This would have required volcanic eruptions traveling at about 30 miles per hour then spewing the diamonds across the surface. The main reason scientists believe the process would have occurred with such speed is because if diamonds were subjected to the intense lava for extended periods of time, then they would have formed into graphite on the way up.

After volcanic eruptions brought the diamonds to the surface, they became contained in a material called Kimberlite. This is essentially cooled volcanic rock. When sealed inside of Kimberlite, they can maintain their natural hard and clear form.

One aspect of diamond creation that researchers still struggle to understand is just how long it takes them to form naturally. Since exact conditions of natural diamond formation are near impossible to replicate in a lab, the best determination method is carbon dating. Dating diamonds in this way has resulted in an estimation of between hundreds of millions to billions of years.

The diamond formation process along with a few diamond facts are laid out in more simplicity in the infographic below.
How Do Diamonds Really Form? (Not From Coal!)

[Image Source: Short Sleeve and Tie Club]

Synthetic Diamonds

Synthetic diamonds are grown in an environment that artificially replicates the pressure and temperature of diamond's natural formation environment. There are two main ways to make synthetic diamonds, one involving pressure and temperature, and the other involving chemicals.

How Do Diamonds Really Form? (Not From Coal!)

[Image Source: Pixabay]

HPTP or high-pressure high temperature is the main method of making synthetic diamonds. A piece of graphite is placed within a pressure chamber. This pressure chamber is then ramped up to 725,000 psi and temps over 2,200˚F. Within a few days of being subjected to this environment, a diamond can form. To kickstart the reaction, scientists have to add a trace amount of metal solution to the graphite. Due to this added solution, diamonds produced in this method are not quite as pure and are used for industrial purposes.

The second growth method for diamonds is chemical vapor based. It uses a process called chemical vapor deposition which creates the perfect diamond – more perfect than found in nature. In this method, a seed diamond is placed inside of a vacuum chamber. This seed diamond is usually an infinitesimally small piece of natural diamond. Once, inside the vacuum chamber, the diamond is subjected to microwave rays and methane and hydrogen are pumped in. The gasses are then heated to over 2,000˚F while the vacuum chamber supplies the pressure. The gas atoms stick to the seed diamond and form a perfect sheet of diamond within a day.

Synthetic diamonds produced through chemical vapor deposition are so similar to natural diamonds that even to experts, they are almost indistinguishable. This is ultimately due to the fact that structurally and chemically, the resultant diamonds are exactly the same. Many jewelers may mistake synthetic diamonds for real ones, however, the mistakes rarely ever occur the other way around.

De Beers Diamond Cartel

It would be near impossible to discuss how diamonds are formed without at least mentioning the De Beers Diamond Cartel. Up until the mid-1800s diamonds were actually rather rare and valuable. However, the discovery of large diamond deposits resulted in significant mining effort that lead to a flood of natural diamonds on the market. The De Beers diamond company was formed soon after the rush to mine diamonds, and they consolidated all mining operations to create a monopoly on the trade and sale of the gem.

This monopoly has continued since the company's formation. Most famously, in 1930s, as diamond prices fell due to lack of demand and increased supply, De Beers began their famous marketing campaign: "A Diamond is Forever." It was this campaign that cemented diamonds into pop culture and is the main reason why they are the stone of choice for engagement rings and other jewelry across the world. This advertising campaign sought to convince the public that the size of diamond you bought directly related to the love you had for your spouse, and through movie stars and pop culture, it did just that.

How Do Diamonds Really Form? (Not From Coal!)

[Image Source: Pixabay]

Diamonds have always been valuable to humans whether naturally through lack of supply or artificially through ingenious marketing. For the scientific community, they continue to play a large role as their material characteristics are unmatched. Whether on your wife's hand or on the head of a powerful cutting tool, diamonds surround our world in ways generations of past never could have expected.

Sources: SarineLive ScienceDMIABusiness Insider