How Green is Green?
Of the more than 5,000 known mineral species, only 130 or so have ever been cut into gemstones. Of this number, not all are durable enough to withstand ordinary wear, so in practice only about 40 to 60 possess sufficient beauty and rarity, along with durability, to be commonly in use as gemstones. All of them are defined by their chemical composition and crystal structure. They are also characterized by the way they interact with the energy of light (whether transparent, translucent, or opaque). We see this interaction as the properties of brilliance, fire and sparkle, and optics is the science that studies them, as well as color itself.
The Four C's -- color, clarity, quality of cut, and carat weight -- apply to all gemstones, although diamond is the only one for which they have been codified into a universally accepted grading system. Diamond is the only gemstone made of just one element (carbon), and, as such, has the potential to crystallize with the greatest purity (that is, the highest clarity), and the most transparency and the greatest hardness as well. Some experts speak of another "C," called "crystal," which means transparency. In diamond, the three top grades (D, E, and F) all fall into what is called the colorless range; another way to think of them is as degrees of transparency.
The beauty, durability and rarity of colored gemstones can also be related to the Four C's. First, they are judged by their color, and second, by their liveliness, or what is called brilliance in a diamond. Sometimes this is called "life," and it is created primarily by how it is cut, the same as with a diamond. Almost every colored stone species has its own traditional "language" of color, such as “pigeon blood” ruby or “cornflower blue” sapphire.
Colored stone sources are scattered all over the world. Colored stone markets are smaller than those for diamond, because, as soon as something has discernible color, individual preferences reduce its appeal. Because of both of these factors, colored stone prices tend to be more chaotic and subjective. With the rise of middle classes in countries where colored stones have been valued longer and more highly than in ours, colored gemstones are growing more popular all the time. Maybe someday there will be the near-universal grading language that has existed for diamonds since GIA first introduced it in the 1950s. For now, we depend on a handful of prestigious laboratories, including GIA, to identify and describe these stones, each one using its own terms.
This demand and improved technology are why more and more gemstones are treated to enhance apparent color and clarity. Some methods have been around for thousands of years and others are more recent. Some are universally accepted (heat treatment of almost all aquamarine and tanzanite, for example). Others are not (the recent plague of lead glass-filled ruby, for example). All should be disclosed to the buyer. A few are only done with the intent to deceive (such as adding green dye to jade).
It has been said that "nothing greens greener" than emerald. But what does that look like? Only a few people get to see enough emeralds to know. You should buy not only from someone whose eyes are experienced, but who can also help you make the comparisons yourself, by showing you green, greener and greenest. I will gladly lend you my connoisseur's eye, so please contact me.