What is it about emeralds that so captivates people? After all, among the most prized gemstones, emerald is the most included, and other green gems (tsavorite garnets, chrome tourmalines, and chrome diopsides) match emerald’s intense, saturated color. What, then, accounts for its continuing popularity? The answer is history.

Among the green jewels, emeralds arrived first. They’ve been around for at least 2,300 years, and because of their long history, they’re common in lore and literature. We know, for example, that Cleopatra’s emerald mines were located southeast of Cairo.

“Green was regarded as the color most beneficial to sight,” writes George Kunz in The Curious Lore of Precious Stones. Emeralds were worn over the eyes so one would see “the beautiful green fields, upon which the tired eye rests so willingly … when sight has been unduly strained or fatigued.” Skeptical? Hold an emerald up to your eye. You’ll experience the calming effect attributed to it in folklore.

Color variations. Emerald’s green color can be modified by yellow, blue, or gray. Gems can be intensely saturated or mildly so, light or dark or any gradation in between. Like most colored gems, the brighter and more saturated an emerald’s color, the more desirable the stone. There’s debate about whether the bluish-green, yellowish-green, or pure green hue is the most desirable. Muzo and Chivor, probably the two most important mining areas in Colombia, typically produce bluish emeralds, which supports the case for bluish-green.

Emeralds may be light in color, but never pale. “Light” vs. “pale” is a judgment call, but a pale green gem that lacks saturated color is categorized as “green beryl”—gemologically, it’s not an emerald. (Emerald is one of several varieties of beryl.)

Qualities. Emerald’s green doesn’t come easily. The chemical elements that impart the color, mainly chromium and vanadium, don’t fit comfortably in beryl’s purest chemical structure. Thus, the factors responsible for emerald’s color are also responsible for the inclusions commonly seen in the gem. To borrow a phrase, you can’t have one without the other.

For thousands of years, gem lovers have accepted those moss-like (or tree-like) inclusions racing across the stone. And today, many jewelers romanticize them as the emerald’s jardin, the French word for garden.

Origin. The gem literature cites no emerald deposit other than the Egyptian mine until the 1500s, when Spanish conquistadors discovered emeralds in Colombia. Emeralds may have been found in India first, but there’s little written confirmation. More than likely, references to Indian emeralds were actually reports of imported Egyptian gems. It’s possible, however, that India has been a source of emeralds since 1500 b.c.

Colombia, whose gems generally rank highest in value, is the most important source of emeralds today. But emeralds from Zambia and Afghanistan are winning praise from international gem dealers and selling for prices approaching those of Colombian gems. The world’s largest producer is Brazil, whose product is generally of second-level quality. The mine closest to home is in Hiddenite, N.C. The occasional discovery of Brazilian-like emeralds there has kept mining hopes alive for tourists and local gem hunters.

Value. If real estate’s value depends on location, location, location, emerald’s depends on color, color, color. Subtle variations can dramatically affect value. Because an emerald’s value is based almost solely on color, it is by far the most difficult gem to price consistently.

The word “Colombian” attached to an emerald can boost a gem’s value, since Colombian emeralds are presumed to possess fine color. In truth, however, Colombia produces emeralds that span the range of color qualities, so it’s imperative to examine each gem.

Pricing. According to The Guide, Fall/Winter 1999-2000, fine-quality emeralds weighing 1 ct. to 2 cts. range in price from $800-$1,250 per carat to $1,250-$2,000 per carat. Fine-quality emeralds weighing 2 cts. to 3 cts. range from $1,250-$2,000 per carat to $2,000-$3,900 per carat.

Enhancement disclosure. If you’re selling an emerald that’s been treated—and the vast majority have been—always inform the customer. If possible, tell what kind of enhancement has been used and specify its durability. To instill confidence, offer a guarantee, such as a re-enhancement service if the treatment isn’t permanent. Have the customer sign a statement acknowledging that she understands why an enhancement has been used.

Consider sending the stone to a qualified gem lab to determine the type and extent of enhancement. If your customer demands a “natural” or untreated emerald, tell her such gems are available but difficult to find. (You can, however, have a slightly enhanced gem cleaned of foreign material, restoring its natural state.)

Care and cleaning. Handle with care any emeralds that have been enhanced with common treatments such as cedarwood oil or Opticon—no ultrasonic cleaning for these beauties. You can, however, use ultrasonic waves—and even steam—on emeralds treated with “Gematrat” from Arthur Groom & Co., New York. Gematrat is a stable and permanent enhancement.

Bench settings and precautions. Because most emeralds contain minute fissures, bench jewelers should use minimal force during the setting process. Masked fissures can hide in corners or edges, too, so be sure to handle all settings with great care.

Recommended reading. For more information, see the following:

Gary Bowersox, “Emeralds of the Panjshir Valley, Afghanistan,” Gems & Gemology, Spring 1991, p. 26.

Gary Roskin, “Last Chance for Colombian Emeralds?” JCK, May 1998, p. 100.

Mary L. Johnson, Shane Elen, and Sam Muhlmeister, “On the Identification of Various Emerald Filling Substances,” Gems & Gemology, Summer 1999, p. 82.