Emeralds are a type of beryl, a mineral composed of beryllium, aluminum, silicon, and oxygen. These elements are found in the continental crust, so the colorless beryls normally found are not very rare. As the earth was forming, beryllium migrated to the earth’s crust while chromium moved into the earth’s mantle. There is typically no reason for either of these elements to come into contact. They are members of different chemical families that separated to different parts of the earth, billions of years ago. Emeralds get their green color because some of the aluminum atoms in the beryl crystal are replaced primarily by chromium atoms. This slight difference is what makes emeralds so rare.

In Colombia, emeralds are found within layers of black shale. These sediments were deposited on the floor of a shallow inland sea about 100 million years ago. The shale contains everything that washed off the various rocks that made up the surrounding land - including most of the ingredients of emeralds. Two times in the last 100 million years, there have been surges in the continental plates that brought together all the ingredients needed to form Colombian emeralds. The Atlantic Ocean was expanding and pushed South America against the Pacific. The Andes were raised, causing the thick stack of black sediment under the shallow sea to buckle. Large sloping faults formed several miles down in the sediments and hot water was squeezed out of them, escaping upward along the faults. The superheated water moved through the faults and dissolved the emerald ingredients. Finally, it pooled under a layer of especially impermeable shale until the pressure shattered that layer. The hot solution shot up through empty cracks in the calcite veins and cooled. As it cooled, emerald crystals began to grow immediately. The emeralds grew unconstrained, without the impurities that often cloud emeralds found in other parts of the world.

Emeralds, among the rarest of gems, are always found with natural inclusions. The reason for the formation of these inclusions is a mystery that scientists have yet to solve. It is very likely that the chemistry of emeralds, composed of aluminum and beryllium, goes through a disruptive substitution of larger chromium atoms that succeed in imparting a deeper green than otherwise would be possible. There is, however, a trade-off for gaining incomparable color. The addition of very minute amounts of chromium needed for the natural “greening” of emerald causes the crystal structure to strain to accommodate the atoms of this trace element - or so it is theorized.

All emeralds that are used for jewelry go through the same six part enhancement process to become the gemstones we know. The steps are sawing, preforming, cutting, polishing, cleaning, and clarity enhancing. Virtually all emeralds require the process of clarity enhancement. This process involves immersing the emerald into a colorless or near-colorless medium. An infinitesmally small amount of the clarity enhancing medium penetrates open fissures. The volume is so small that it is usually not measurable by weight (typically as little as 1/100,000 of a gram). It should be assumed that every emerald has been processed in this manner unless it has an accompanying laboratory report indicating that there is no evidence of a clarity enhancement medium. Such extraordinarily rare gems command a considerable premium.

Agents used for clarity enhancement are colorless or near-colorless: oils (fair stability), prepolymers and uncatalyzed resins (fair to good stability), paraffins (good stability), and polymers (excellent stability). Using any of the above, except for polymers, to enhance an emerald produces good initial results, but there are some limitations to the effectiveness of these enhancements. Over time, the agents will escape the fissures in the emerald and again reveal the inclusions. Cleaning an emerald using traditional jewelry cleaning products and techniques will also serve to remove these agents from the fissures. The emerald will need to be enhanced, occasionally by “oiling”, to maintain its beauty.