Diamond - known to the ancients as adamantine - is what is known as an allotrope of carbon, and in chemical terms, is identical to common forms of coal and graphite. The difference lies not in chemical composition, but rather in how the molecules are arranged.
Diamonds form far deeper beneath the earth's surface than coal or graphite; the carbon is subjected to extraordinarily higher pressures (up to 440 tons per square inch) and temperatures (as much as 2300 degrees Fahrenheit). This causes the molecules to be bonded to each other in a tetrahedral arrangement, accounting both for the hardness of diamond and the eight-sided shape in which they occur.
Shades of Difference
Colored diamonds are ones in which this molecular arrangement has been contaminated by a chemical reaction with some other element. A diamond that is made from pure carbon and has no structural flaws would be as perfectly transparent as pure water ice. However, no such 100% flawless diamonds have ever been found in nature.
Colored diamonds range in color from pale blue and storm gray to dark amber and even black. Pink, purple, reds and oranges have also been found. The color depends on the nature of the chemical impurity; amber and brown diamonds result from nitrogen; when internal flaws are present, they may be pink or red. A grey coloration is caused by boron, whereas a deep blue diamond may be the result of hydrogen.
Are They More Valuable?
Colored diamonds are not necessarily more valuable than clear or colorless ones, although they may be. If a collection of loose diamonds includes gemstones with a yellowish tinge, they may have less value; jewelry retailers often discount the price of such gems. One the other hand, pink and red diamonds are exceedingly rare, and command high prices on the open market when they are available at all.
Like their clear counterparts, colored diamonds have a unique grading system used by gemologists when analyzing and evaluating such stones. These range from "faint" on one end, to "fancy" in the mid range, and "fancy dark" for those with the most intense coloration.
Famous Examples
The Hope Diamond is a blue diamond that is currently on display at the Smithsonian Institute. One of the most valuable diamonds on earth (and the inspiration for a series of comedy films featuring a bumbling French detective) is the Dar-I-Nur, an enormous pink diamond that is part of the Persian Crown Jewels.
- including a "chameleon" diamond that changes color - are part of the Aurora Collection, which has published photo images of their gems and can be seen at the London Museum of Natural History.
