Black Diamonds - FAQ

Black Diamond - Origin and Mineral Properties

Where are black diamonds found?

Black diamond crystal from RussiaBlack diamonds are found mainly in two places on earth - Brazil and Africa, specifically the Central African Republic. It's interesting to note that in prehistoric times, prior to the continental drift, these two areas were adjacent to each other, so in that sense black diamonds appear to have originated from this one place on the earth. They are also found exclusively in alluvial deposits - deposits and sediment created by a river or other source of running water.

How are black diamonds different from other diamonds?

Natural black diamonds differ from other kinds of diamonds in several respects:

1) They're porous
2) Most of them are very tiny. Larger black diamonds, instead of being one large crystal, have a polycrystalline structure, meaning they're made up of millions of small crystals which are all stuck together.
3) They are highly included.
4) They are found almost exclusively in two locations- other types of diamonds are found throughout the world. Furthermore, diamonds are normally found in the mineral kimbertite. Black diamonds are found in newer and different deposits of a sedimentary nature.
5) They have a different carbon isotope (same chemical element with different atomic weights and physical properties) than other diamonds. These isotopes are commonly found in the earth's crust, rather than inside the earth (mantle), where other diamonds originated.

What makes them black?

Natural black diamonds are black because their unique crystalline structure absorbs light.

Diamonds can also be made black through color treatment. (See below.)

What is a carbonado?

A carbonado, also called a carbon, is another name for a black diamond which is not gem quality. The name originates from their burnt or carbonized appearance. [click to see a picture]

How were natural black diamonds formed?

Good question! There are four theories on this, none of which have yet been formally accepted as fact.

1) They were created by some sort of meteoric impact.
2) They were created by pressure within the earth, just like other diamonds (this was the first theory, it is no longer believed to be the true).
3) They were created by radiation - spontaneous fission of uranium and thorium
4) They are from ... outer space! (More on that below)

Are black diamonds harder than other diamonds?

Yes and no. Like other diamonds, they have a hardness of 10 (the hardest) on the Moh's scale, however stones with a dense polycrystalline (made up of multiple crystals) structure behave as if they were harder and are subsequently much more difficult to cut and polish.

Are black diamonds from outer space?

Sounds like a crazy question, doesn't it? Strange as it seems, there's some speculation about this in the scientific community,, and potential evidence, that they traveled to earth via an asteroid! There are articles discussing this theory in more depth at the PBS/NOVA website and at Science Daily.

What are Alaskan Black Diamonds?

Alaskan black diamonds is a popular name for the stone, Hematite. These are not genuine diamonds. Hematite is a gray to black stone with a metallic sheen. It is an attractive stone in its own right , but related to a diamond.

Black Diamonds in Jewelry

Why are black diamonds difficult to cut and polish?

Natural black diamonds typically have a different crystal structure than any other type of diamond. Where an ordinary diamonds is composed of a single crystal, a black diamond the same size can be made up of millions of tiny crystals. This not only makes them extremely difficult to cut, and at the same time more fragile and less predictable for a diamond cutter to work with.

Are black diamonds transparent, translucent or opaque?

Natural ones can be opaque, though some black diamonds (more properly dark gray ones) have some transparency.

Color enhanced black diamonds are not opaque.

Do black diamonds "sparkle" like other diamonds?

Not exactly. Like marble or onyx, the beauty of a black diamond lies more in it's surface polish. They absorb light, rather than reflect it.

How do the prices of black diamonds compare to white diamonds?

The relative value depends upon the diamonds themselves. Treated black diamonds tend to be less expensive than colorless diamonds of a similar size because the stones selected to undergo the color enhancement process are usually of a lower quality (in color or clarity) to begin with.

On the other hand, a high-quality, natural black diamond would generally be more costly than a colorless diamond of a similar size and characteristics due to the rarity of the color.

Enhanced Black Diamonds

What are "enhanced" black diamonds?

Enhanced black diamonds are ordinary diamonds, usually low-color stones, which have been treated in some manner to shift their color to black.

How are diamonds enhanced to become black?

There are two different processes that can be used to create a black diamond, heat treatment and irradiation.

In heat treatment, the diamond is exposed to temperatures around 1000 degrees centigrade, which creates graphite residue inside the crystal and makes it appear an opaque black.

The most common process used today to produce enhanced black diamonds is irradiation. Irradiation modifies the crystal lattice of the stone, making it appear black. An irradiated diamond will have a lab certificate saying that it has been "treated".

Nearly all black diamond jewelry currently sold through retail channels is made with color treated (irradiated) diamonds. One way to tell is to examine the diamond using a very bright light source, like a fiber-optic light. If you look closely, you can see that irradiated black diamonds are actually a very dark shade of green.

Are irradiation-enhanced diamonds safe to wear?

Yes. Modern methods of irradiation leave no harmful residue on the diamond. Irradiation creates a safe and affordable alternative to rare and extremely expensive naturally colored diamonds


Attribution for black diamond crystal photograph: Rob Lavinsky, iRocks.comCC-BY-SA-3.0.