Fancy Color Diamonds: What Gives Them Color?

Sofia Temmuz 07, 2021

What gives a diamond color? Typically people think about diamonds as being colorless. The more colorless it is, the more valuable it tends to be. The only exception to that is if the diamonds have an intense enough color that they’re called a fancy color diamond, which can add tremendously to the price. The colors are always due to some impurity or defect in the diamond’s structure. It’s the impurities that give rise to colors not only in most diamonds, but most gem materials.

In the case of the blue diamonds, like the Hope Diamond, it’s a little bit of boron that happened to get trapped in the crystal structure as it was forming that gives the blue color. Blue is an extremely rare color. Maybe, at most, one out of 200,000 diamonds found in the world has any hint of a blue color to it, and typically it’s a very pale blue.

If some nitrogen is replacing some of the carbon atoms in the structure, that little bit of nitrogen can color the diamond a yellowish color. It’s thought that most yellowish to maybe brownish-yellow diamonds probably get their color because of some kind of defect structure related to nitrogen impurities. The Tiffany Yellow diamond is a famous example.

Green diamonds are thought to form mostly because of natural radiation in the rocks where the diamonds are found. The radiation produces defects, mistakes in the crystal structure of the diamond, and these defects can trap electrons that will interact with light to produce the green color. Interestingly, most green diamonds do not have a green body color. They have sort of a green outer coating because the green color originates from the radiation that is in the rocks surrounding the diamonds after they’ve been brought to the surface. Because it’s coming from the rock surrounding it, it tends to be most intense at the surface and only in some cases will it completely penetrate the whole diamond. So green is a very unusual color. The Dresden Green diamond is an example of a natural green diamond.

Pinkish to reddish diamonds are thought to be colored by some kind of mechanical defect or stresses in the diamond that may have been induced during the travel to the surface or by tectonic forces working on the rocks after they’re brought to the surface. These defects are thought to trap electrons in such a way that they interact with the light to produce pink and red colors. A famous example of a pink diamond is the Steinmetz Pink. Red diamonds are the rarest of all and are usually very small. A rare 1.56 fancy red diamond, the Argyle Phoenix, was discovered just this year.

Diamonds also come in all sorts of shades of browns to yellows to oranges, which are combinations of these various basic causes of color.