How Colored Diamonds are Formed
A perfect diamond by definition would be a transparent diamond, a diamond with out any color that shows no fluorescence to UV light. These diamonds are often referred to as d-flawless, and extremely rare as the conditions for their formation are not often found in nature. In actuality, the vast majority of diamonds form with small impurities or structural defects which are know to disrupt the flow of light in the stone causing some interesting results. These imperfections cause parts of the visible-light spectrum to refract or absorb differently which results in the appearance of color.
The most common of these imperfections is caused when trace elements of nitrogen interact with the carbon elements during the diamond’s formation. This results in the creation of a yellow diamond. It is widely believed that yellow diamonds are less desirable and valuable than a white diamonds, as the manifestation of this imperfection typically results in faintly colored yellow or off-white diamonds. The Gemological Institute of America (GIA) considers low saturation yellow diamonds in the normal color range, and as such their value is limited. The presence of low levels of nitrogen is common during formation, but higher levels are not. In higher concentration, the crystal structure forms with a defect that causes large absorption of the blue and violet region of the visible light spectrum, creating a beautiful intensely colored yellow diamond. As these conditions are extremely rare, very few exist, and as a result fancy yellow diamonds are known to fetch spectacular prices at auction.
Blue diamonds are also know to form due to the presence of trace elements during the formation of the crystalline structure. In this case two independent elements can create the color. In the first, it is the presence of boron atoms that cause the structure to change. In these rare cases the carbon atom can be replaced by the boron atom. In the second, if the diamond forms in a rich hydrogen environment the crystal to form will absorb the red, green, and orange colors in the visible light spectrum leaving only blue. While their color is typically a subtle blue, in rare cases a more vibrant blue has been noted. Blue colored diamonds are very rare, however some believe they may become more readily available due to the emergence of mines producing the stones in Botswana.
While yellow and blue colored diamonds are known to form due to the presence of trace elements, this is not the only ways a colored diamond can be created. In the case of green diamonds it is the presence of natural irradiation during and after formation that result in the development of color. The size of the stone, as well as the duration of exposure, and the type radiation will determine the shade and intensity of the color of these stones. Exposure to Alpha and beta rays will result in faint coloring, but prolonged exposure to gamma and neutron radiation can produce spectacular greens. Natural green diamonds are also often noted to have radiation spots, these are often left on an unpolished part of the girdle in an attempt to provide incontrovertible proof that the diamond’s color is the result of natural irradiation. Green diamonds can also be found with a yellowish hue due to the presence of trace levels of nitrogen or hydrogen during formation. Diamonds with such a yellowish hue, are commonly refer to as “Chartreuse” diamonds.
The final imperfection causing color is the result of what is referred to as plastic deformation. This occurs when a diamond experiences tensile stress due to it’s environment. The process sees a diamond’s atomic structure dislocated and realigned through mechanical twinning. The result is a disruption of the nitrogen centers in a diamond, manifesting itself as a color zone called the “pink grain” inside the stone. Pink diamonds are some of the rarest colored diamonds found on earth. So rare in fact that very few people in the diamond industry will ever even see them. Red diamonds are also thought to be created by plastic deformation, but are even more rare. So rare in fact, very little has been discerned about their formation, where they can be found, or the range of colors that might exist.
Gem quality diamonds are for the most part colorless, and the presence of light discoloration can devalue a stone. At the same time specific colors, and the intensity of their coloration can be rare and beautiful making them inherently valuable. Interestingly enough it’s the same imperfections in formation that can define one stone’s price, and another stone as priceless.
Read the next article: How Diamonds Are Processed