Last updated on January 15, 2021
We are used to thinking of diamonds as white sparkling stones. But did you know that there are also fancy black diamonds? These are among the most popular choice of coloured diamonds, but there are a lot of rumours about them. So let’s find out what is the reality.
What Are Natural Black Diamonds?
Natural black diamonds, also known as “carbonado”, have the same chemical composition as white diamonds. However, the crystal structure of black diamonds is different, meaning they consist of many small crystals that stuck together in random formation instead of a solid cristal with identifiable natural lines.
Natural black diamonds have an extremely high amount of inclusions such as graphite, pyrite or hematite, causing them to differ in colour. In fact, the real body colour of natural black diamonds may range from near-colourless to brown or olive green, but the concentration of numerous inclusions makes them appear black.
Natural black diamonds are usually completely opaque with a high lustre which gives them a metallic appearance.
Although black diamonds are still graded 10 on the Mohs scale of mineral hardness, they are known to be even harder than the majority of diamonds. This unparalleled durability is the result of the differences in their structure which is why these gems were used for a variety of functions before being applied in jewellery.
What Are Treated Black Diamonds?
Treated black diamonds are created in labs by treating white diamonds that are usually of extremely low value because of the high amount of inclusions. Heat or radiation treatment graphitizes the fractures and turns the colour of these gems to black.
As you might guess, treated black diamonds are more affordable and common than naturally occurring ones. Since natural black diamonds are relatively rare, you should know that if you are about to buy a black diamond for an affordable price, it is very likely to be a white diamond that has been treated.
How Are Black Diamonds Graded?
In contrast to other coloured diamonds, black diamonds are found in only one colour grade: fancy black. Moreover, since most black diamonds are heavily included they cannot be graded on the GIA clarity scale as well. That is why instead of a grading report (certificate), GIA issues a Coloured Diamond Identification and Origin Report where black diamonds are described as fancy black and their colour origin is noted as natural or treated.
As black diamonds are opaque there will be no mention about the polish and symmetry grades, only colour grade, colour origin, carat weight and measurements.
It is highly recommended to purchase black diamonds that have been graded by reputable laboratories as this is the only way to know for sure if the gem is natural or treated.
Are Black Diamonds Low-Quality Stones?
The colour of black diamonds is not only due to their inclusions but also due to their unique structure. The structure affects how they reflect light, which is mostly absorbed by the stone. Black diamonds do not display any brilliance or sparkle.
Treated black diamonds, in their turn, owe their colour to the treatment and not the structure. Whether the original white diamond that has been treated was of high quality is a different matter. But let’s agree, it is very unlikely that someone will take an expensive white diamond of the highest quality and change the colour to sell it for less money.
Just keep in mind that regardless of the origin, such stones have a very low clarity grade because of their colour and structure. However, traditional quality guidelines used to evaluate white diamonds do not apply to black diamonds. That’s why the term “low quality” doesn’t make sense when used for black diamonds.