Colored diamonds, often called fancy diamonds or fancy colored diamonds in the industry, carry all the same attributes as the more well-known colorless diamond. Made from the same heat and pressure over many years deep in the Earth, they are carbon that has been formed into rough diamond crystals. Though to achieve the variety of colors, there are a few causes that are responsible.
The most common color-causing event in diamonds occurs when an atom of another element replaces a carbon atom in the crystal structure. The substitution of another element causes visible light wavelengths to be transmitted and absorbed differently. So, the presence of nitrogen can cause a yellow diamond appearance, the presence of boron a blue diamond, and the presence of hydrogen a violet diamond.
Another event is the result of exposure to naturally occurring radioactive mineral grains over the many years of formation. These particles have the ability to knock carbon atoms out of the crystal formation causing a vacancy. This vacancy can then allow for more absorption of red wavelengths and a stronger transmission of green wavelengths. This vacancy event is what creates natural green diamonds.
The next event produces the opposite outcome of the previous example, and is also what causes earthquakes and volcanic eruptions. Diamonds that form near areas of the Earth’s interior, where there’s higher plate tectonic activity, can cause a diamond’s crystal structure to slip slightly out of alignment. This occurs across surfaces within the diamond called “glide planes” and while they don’t damage the integrity of the diamond, they change the way light passes through. This event commonly produces brown diamonds, and on very rare occasions, pink or red diamonds.
Mineral inclusions are the final event to cause the appearance of color in diamonds. A high density of inclusions that heavily interfere with the passage of light is responsible for producing some of the most popular colored diamond hues: grey, salt and pepper, and black. The inclusions usually consist of opaque minerals like graphite, hematite, and pyrite. When the minerals have a small particle size and are evenly distributed, the diamond can present an opaque appearance and highly reflective surface.
Black diamonds will present the most dense mineral inclusions with even distribution, while grey diamonds will feature less dense inclusions but still a fairly even placement. Salt and pepper diamonds feature patches of these dark minerals mixed among the more white or colorless areas.