The dark side of the stone: A look at black diamonds

Untreated black diamonds

Here is an image of an incredible untreated 1.11 carat rose-cut pear-shaped black diamond from Krikawa. Look closely and you will observe that the stone is not a transparent, "glassy" black but seems filled with something mysterious. That inner texture is a result of the inclusions.

Here is an image of an incredible untreated 1.11 carat rose-cut pear-shaped black diamond from Krikawa. Look closely and you will observe that the stone is not a transparent, "glassy" black but seems filled with something mysterious. That inner texture is a result of the inclusions.

Naturally black diamonds are colored by an excessive amount of shadowy inclusions composed of graphite, magnetite, hematite, or iron.

Natural black diamonds (in contrast to color-treated black diamonds) have a well-deserved reputation for being troublesome to work with. They are composed of many diamond crystals and they are filled with inclusions. The qualities that make a naturally black diamond so lovely also make it difficult to cut and polish. So when you see a beautiful specimen, you should know that not only is it rare -- but it also required a high level of expertise and a great deal of time to cut and polish in order to bring out its beauty.

Numerous eye-visible breaks on the surface of this natural color black diamond is a common phenomenon. This image is from the Gemological Institute of America.

Numerous eye-visible breaks on the surface of this natural color black diamond is a common phenomenon. This image is from the Gemological Institute of America.

Treated black diamonds

Because natural black diamonds are so difficult and time-consuming for lapidaries to cut and polish, manufacturers often irradiate industrial-grade diamonds to change their color so that they appear to be black. But surprise! Irradiated black diamonds are actually a very deep, very dark green!

In this image from the Gemological Institute of America, you can see that artificially irradiated "black-appearing" diamonds can reveal a dark green coloration through thin, relatively transparent edges when examined with intense illumination.

In this image from the Gemological Institute of America, you can see that artificially irradiated "black-appearing" diamonds can reveal a dark green coloration through thin, relatively transparent edges when examined with intense illumination.

The majority of black diamonds on the market are natural diamonds that have been color treated, which mean they were mined from the earth and irradiated -- or exposed to a strong radioactive and heat treatment that darkens the stone’s color.

Mysterious origins

Some scientists believe that black diamonds come from outer space.

It's true. Some scientists suggest that Earth's black diamonds came from a supernova which occurred at least 3.8 billion years ago. After coalescing and wandering through outer space for about one and a half billion years, part of it fell to Earth in the form of a meteorite somewhere around 2.3 billion years ago. They think it possibly fragmented during entry into our atmosphere and landed in a region which would later split into Brazil and the Central African Republic... the only two known locations of black diamond deposits.

However, there are many hypotheses on the origins of naturally-occurring black diamonds. Here are a few:

1. Direct conversion of organic carbon under high-pressure conditions in the Earth's interior, the most common hypothesis for diamond formation.
2. Shock metamorphism induced by meteoric impact at the Earth's surface.
3. Radiation-induced diamond formation by spontaneous fission of uranium and thorium.
4. Formation inside an earlier-generation giant star in our area, that long ago exploded in a supernova.
5. An origin in interstellar space, due to the impact of an asteroid, rather than being thrown from within an exploding star..

Shown here is a collection of faceted natural black diamonds from Alexis Russell. Notice the interesting shapes, complex inclusions, and range of hue.  

Shown here is a collection of faceted natural black diamonds from Alexis Russell. Notice the interesting shapes, complex inclusions, and range of hue.
 

Famous black diamonds

Perhaps the most famous natural black diamond is the Black Orlov.

Also known as the Eye of Brahma Diamond, it weighs a stupendous 67.50 carats. But imagine! The diamond was originally 195 carats when it was discovered in the early 1800s in India. Like many stones that made their way from India to Europe, it was supposedly set as one of the eyes in a statue of a Hindu god. And when it was stolen (in this case by a monk), the stone became accursed -- causing at least three of its owners to jump to their deaths. When Charles F. Winson acquired the stone, he had it cut into three pieces hoping to break the curse -- or at least lessen its effect. Thus the Black Orlov was set into a brooch with 108 white diamonds and suspended from a necklace of 124 more diamonds.

The current owner feels "pretty confident that the curse is broken."

And another legendary black diamond: the Spirit of Grisogono.

At 312.24 carats the Spirit of de Grisogono is the world’s largest black diamond, and world’s 5th largest diamond. A formidable ring in a unique, mesmerizing white gold mounting, it is set with 702 white diamonds weighing a total of 36.69 carats. This diamond originally had a rough weight of 587 carats and was mined in the nineties in west Central Africa. It was later brought to Switzerland, where it was cut by Fawaz Gruosi using the traditional Mogul diamond cutting technique. There is no information on the whereabouts of the precious stone or the identity of its current owner, although it is thought to have been sold onto a private client.

Sources

Alexis Russell: http://www.alexisrussell.com/

Geology IN: http://www.geologyin.com/

GIA 4Cs Blog: http://4csblog.gia.edu/

Krikawa's jewelry design blog (The Ring Leader): http://www.krikawa.com/blog/