The miracle of a natural diamond – how diamonds are formed

How are colored diamonds made?

Although extremely rare, if a diamond contains just one speck of a foreign atom that is not carbon, this can change the color of the diamond. Discover how colored diamonds are formed.

Did you know

Red diamonds are the rarest colored diamond.

1

Deep in the earth

Natural diamonds were born deep below the earth’s surface in environments of extreme pressure and temperature.

At depths of over 120km, through intense heat of between 900°C and 1300°C, pressures of 45 kbar and above and over millions and often billions of years, this incredible miracle happens – carbon crystallizes to form diamonds.

In order to continue this extraordinary journey, the diamonds need to be released from the intense pressure and heat under which they are formed in order to embark upon their voyage to the earth’s surface.

This happens when an event deep in the earth causes a part of the mantle to melt into magma which then erupts rapidly to the surface of the earth, transporting diamonds from great depths. As the magma cools, it hardens to form the rock called kimberlite, mainly in vertical structures known as kimberlite pipes. These are the most significant source of diamonds, accounting for nearly all natural diamonds. However, of the 15% of kimberlite pipes that have been discovered across the world that contain diamonds, only 1% are economically viable, highlighting how truly rare diamonds are.

Did you know

The name Kimberlite derives from the South African town of Kimberley where the first diamonds were found.

2

Tectonic plate movement

Some extremely small diamonds that have been found in ultra-high pressure (UHP) metamorphic rocks in Kazakhstan, China, and Norway. They are thought to have been brought to the earth’s surface by tectonic plate movement during mountain building processes.

Another tectonic process called subduction occurs when one tectonic plate moves under another and is forced to sink, due to gravity, into the mantle. Organic carbon is recycled back into the mantle during this process and may then crystallize into diamonds.

3

Meteorite impact

Throughout its existence, Earth has been hit by meteorites and when there is a large meteorite impact, extreme temperatures and pressures are produced, which are the perfect environment for the formation of diamonds. Diamonds found around meteorite impact sites, e.g. the Popigai crater in Siberia, are tiny and of poor quality.

4

Meteorites in space

Nanodiamonds are diamonds that are a few nanometers (billionths of a meter) in diameter. Researchers have detected large numbers of nanodiamonds around newly formed stars and in some meteorites. These diamonds are too small for use; however, they are a valuable source of information about the composition and formation of our galaxy.

Labgrown diamonds

Not all diamonds are formed naturally. Laboratory grown diamonds or LGDs, sometimes also referred to as artificial diamonds or synthetic diamonds, are made of a man-made material that possesses the same chemical composition and the same basic crystal structure as a natural diamond.

There are two main processes for creating lab grown diamonds, High Pressure High Temperature (HPHT) or Chemical Vapor Deposition (CVD).

HPHT mimics the growth of a natural diamond by creating high pressures and temperatures that are applied to a tiny natural diamond seed upon which further diamond is grown from molten carbon.

CVD, the more commonly used process, again starts with diamond seeds. These seeds are exposed to a gas mixture that is heated to a temperature of around 3000°C in a sealed chamber. The gases then form a plasma and carbon atoms are able to stick to the diamond seed and then crystalize to form a larger diamond.

Lab grown diamonds can be manufactured very quickly - a one carat lab grown diamond can be produced in as little as three to five days. Because lab grown diamonds are mass-produced in batches, they don’t possess the enduring value of natural diamonds, and as technology continues to improve and as lab grown diamonds become more widely available their value is expected to fall.