how are diamonds formed

How Are Diamonds Formed?

These days, jewelry shoppers have the option to buy either a mined or lab-created diamond for that special necklace or engagement ring. Lab-created diamonds look the same as mined diamonds, but there are still a few minor differences between the two, mainly price point. While some may be deterred from purchasing a lab-created diamond because it’s manufactured, diamonds grown in a lab are just as real as ones mined from the Earth.

So, how are diamonds made? Whether the diamond is lab-created or mined determines what the process looks like. Here’s a look at both types of diamonds, so the next time you’re shopping for jewelry, you know you’re buying what you prefer.

How Are Mined Diamonds Formed?

Mined diamonds are carbon deposits originally formed beneath the Earth’s surface millions to billions of years ago. These structures become crystallized, giving them that familiar diamond look, because of the intense heat and pressure they are subjected to many miles below the surface.

The diamonds mined today by people were brought to the surface a long time ago in Earth’s history. While it’s hard to determine a diamond’s exact age, they can take anywhere from days to months to millions of years to materialize.

A diamond’s formation can be disrupted by a change in pressure and temperature. Diamonds require conditions that are suitable for growth—usually at least 2,000 degrees Fahrenheit and a pressure of 725,000 pounds per square inch or more. If these variables are changed or disturbed, a diamond may wait hundreds to millions of years for conditions to become stable enough for them to continue to grow.

Four different methods are responsible for the diamond deposit sites we find near the Earth’s surface today. Let’s take a look at each one.

1. Formation in the Earth’s Mantle

Most diamonds used in engagement rings today are found in diamond mines. These gemstones were originally formed in the upper mantle of the Earth with heat and pressure. During natural events, like volcanic eruptions, diamonds are brought to the surface from the Earth’s mantle.

The volcanic eruptions we see today are minor compared to the deep-source, violent eruptions that must occur for diamonds to move closer to the surface. These eruptions bring lamproite and kimberlite pipes where gemstones are found by tearing out pieces of the mantle and carrying them rapidly to the surface. This sort of intense volcanic eruption is very rare and, therefore, has never been witnessed by modern humans.

Underground mines have been developed in these pipes if they contain an adequate supply of diamonds. These pipes may also contain eroded or weathered diamonds, which are also profitable options since they are contained in sedimentary deposits of coastlines and streams.

2. Formation in Subduction Zones

The plate tectonic process of subduction occurs at convergent plate boundaries where an oceanic plate slides underneath a continental plate. When subduction movement occurs, people may feel the effects in the form of an earthquake on the surface.

Subduction is also a vital process for diamonds to be formed. This type of diamond formation occurs when rocks are subducted deep into the Earth’s mantle from tectonic movement, then later returned with tiny diamonds to the surface. Unlike mantle formation, which requires extreme depth and high temperatures, diamonds formed from subduction can materialize 50 miles below the surface, with temperatures as low as 390 degrees Fahrenheit.

These diamonds also originate from carbonate rocks, such as marble, limestone, dolomite, and possibly plant debris particles found in offshore sediments. Other discoveries have pointed to stones being uncovered in subduction zones and containing traces of the oceanic crust. These traces appear as blue diamonds.

It’s important to note, however, that rocks formed in subduction zones are extremely rare. Currently, no known commercial diamonds have been found from this source and sold by jewelers.

3. Formation at Impact Sites

Earth has been struck by asteroids numerous times in its history. When these asteroids hit the Earth’s surface, extreme pressure and temperatures are produced. This type of intense impact creates sufficient conditions for forming diamonds.

While this process has never been witnessed in the modern era, there have been many discoveries of tiny diamonds found in and around several asteroid impact sites, like the Meteor Crater in Arizona and the Popigai Crater in Siberia. Diamonds found at these locations are extremely small and are considered sub-millimeter diamonds.

4. Formation in Space

High-speed collisions in space between meteorites and other masses can cause diamond formation. Researchers have detected nanodiamonds—diamonds that are billionths of a meter in diameter— formed from carbon sources in some meteorites. Unfortunately, even if it were possible to obtain these diamonds, they would be too small to be used as jewelry gemstones.

diamond formation

Are Diamonds Made from Coal?

A popular belief is that some mined diamonds originated from coal. However, this is highly unlikely. Coal is a sedimentary rock formed from plant debris deposited on the surface of the Earth. Coal is not buried deep enough into the surface to be subjected to the heat and pressure required to make diamonds. Therefore, it is more likely that the carbon deposits that turn into diamonds are sourced from carbon trapped in the Earth’s interior during planet formation or delivered by subduction processes.

How Are Lab-Created Diamonds Made?

If they aren’t mined, then how are diamonds made in a lab? Modern-day technology has allowed jewelers to turn to labs as a legitimate source for diamonds to sell in jewelry stores. Lab-grown diamonds, also called man-made diamonds, are exactly the same as natural diamonds except for the fact that they aren’t formed within the Earth. Lab-created diamonds are made using cutting-edge technology that can mimic the natural diamond forming process.

Therefore, a lab-created diamond is chemically, physically, and visually the same as those found in nature. Manufactured diamonds are grown from a carbon seed. Scientists then replicate the conditions in which natural diamonds are formed using two methods: High Pressure-High Temperature (HPHT) and Chemical Vapor Deposition (CVD).

  • HPHT: There are three different manufacturing processes used for HPHT: a cubic press, a belt press, and a split-sphere press. All three presses can imitate the high pressure and extreme temperatures found in the Earth’s mantle. First, a diamond seed is placed in carbon and then exposed to temperatures as high as 2,000 degrees Fahrenheit and heavily pressurized to 1.5 million pounds per square inch. Once the carbon melts and cools, a crystallized diamond is left behind.
  • CVD: In this diamond-making process, a small diamond seed slice—usually produced from HPHT—is heated to extreme temperatures in a chamber. Gases, like methane, are then put into the chamber to help with diamond formation. When the chamber is filled, the gasses ionize and turn into plasma, breaking molecular bonds and allowing carbon to adhere to the diamond seed. Crystallization then begins, with the final crystallized carbon structure being the same as a mined diamond.

Lab-created diamonds offer many benefits, including the ability to produce a precious stone in large quantities while reducing environmental risks by eliminating mining. You will also get the same quality of stone as a mined diamond, but the price point will be much less expensive.

Additionally, lab-created diamonds are just as unique as mined ones since each one turns out completely different. Labs that manufacture diamonds can replicate the same conditions found underneath the Earth’s surface. Because of this, lab-grown diamonds can be graded using the 4C’s just like mined diamonds.

Noe’s Jewelry is a local jewelry store in Raymore, Missouri, offering a wide selection of diamonds to choose from. Visit our store today or contact us at 816-322-7227 to learn more information.