Emeralds are the closest link between the eye and the deepest recesses of the earth. Unlike ruby or sapphire, which are generally carried by rivers from their original source, emeralds are only found in situ. Fine deposits must be cleared by hand as the use of explosives can destroy the fragile emerald crystals.
While by no means comprehensive, this overview will touch on the gemological properties of emeralds, quality factors, common treatments and significant origins. Our hope is that you leave with a general understanding of the emerald market and a peek into the alluring qualities of this precious stone.
Widely regarded as the definition of green, emerald evokes a sense of spring and represents the idea of rebirth and renewal. For the Mughals, Ottomans, and Persians green was the color of Paradise. The ancient Egyptians also regarded the emerald as being mystical and magical, with its deep green color unlike the green of anything else known to them.
Variations of this rich green color suggest soothing, lush gardens. The oldest known specimens on earth have been dated to 2.97 billion years old. Legend has it that that emerald has the power to make its wearer more intelligent and quick-witted and it was once believed to cure diseases. Today it is the birthstone for the month of May as well as the traditional gift for the 20th and 35th anniversaries.
Mineral, Color & Quality
Emerald is the green to bluish green variety of beryl, a mineral species that also includes aquamarine (pale blue) and morganite (pale pink).
An emerald is a complex combination of beryllium-aluminum silicate, which in its pure state is a colourless crystal. When tiny traces of chromium are added in nature to this beryl, it becomes green and is termed emerald.
The most important measure of quality of an emerald is color. Fine emeralds are described as pure green to bluish green, with vivid color saturation and a tone that is not too dark. The most prized emeralds are highly transparent. Their color should be evenly distributed with no visible color zoning.
Emeralds typically contain inclusions that are visible to the unaided eye. Because of this, eye-clean emeralds are especially valuable because of their rarity.
Slight differences in the amount of chromium will radically alter the depth of green in emerald. Within the green shade of emerald, there are worlds of differences.
While opinions differ on the degree of green that makes one stone an emerald and another a less-valuable ‘green beryl,’ most gemologists and gemological laboratories categorize a stone as ‘green beryl’ when its color is too light to be classified as emerald.
Emerald is a 7.5 – 8 on the Mohs scale of hardness. This makes is more susceptible to scratching than a sapphire or diamond which rank 9 and 10 on the scale. The stone’s relative delicacy requires some special care, such as avoiding exposure to extreme heat, and harsh chemicals.
Setting choices should consider protecting the edges of the gem, to avoid chipping or cracking the stone.
Emerald was one of the most highly prized gemstones in antiquity. The earliest known emerald mine is located in Egypt's Eastern Desert, where mining probably began in the first century BC.
Treatments & Enhancements
It is said as much as 99% of available emeralds are treated in some way. This is because the overwhelming majority of stones have minute surface reaching fractures. These natural inclusions are often treated to improve clarity, making untreated or insignificantly treated gems exceedingly rare and valuable.
The significance of treatment in a stone should always be disclosed to the buyer and the price should be reflective of the stones natural rarity.
It is important to note when purchasing an emerald that the treatment classification is not representative of the natural inclusions within a stone but instead how much foreign substances has entered inside the crystal.
Treatments range from insignificant/minor oiling, to moderate and significant fracture filling treatments.
As far back as Ancient Egypt, the process of fracture filling has been documented in scrolls and ancient texts. Unlike other colored gems that are typically treated with permanent methods of high heat and pressure to improve color and clarity, emeralds would be damaged by such processes. Typically, the preferred method to enhance an emerald is through filling natural fissures and fractures with oils, although more permanent methods do exist.
Natural Cedar Oil
Natural cedar oil is traditionally used as it is colorless and does not interfere with the natural refraction of the gem, meaning light is able to pass through easily. A stone is gently heated to open its surface reaching fissures before being soaked in oil and sometimes treated at low pressure to encourage the oil to penetrate the gem, filling tiny cracks, purifying the tint and helping to conceal inclusions.
Many modern stones have been treated with polymer resins. Polymer is more resistant to wear and more stable however is considered a more extreme treatment. The most significant treatments involved colored polymer resin and oils that artificially enhance the stones hue where it is masqueradeing as a higher priced gem. It is important to note that the hue of these heavily treated stones does not match that of the actual emerald and the dye will likely fade over time. These type of treatments are generally frowned upon in favor of traditional oil treatments.
Oil treatments are not necessarily permanent and stable. Time, heat or improper cleaning can cause the oil to evaporate, change color or leach out of the stone.
Stones can be re-oiled if this occurs. Cedar oil is 100% natural which is why it is the favoured and most traditional form of treating an emerald. A stone with a minimal amount of treatment should never normally require re-oiling.
Many dealers of low quality goods have begun using artificial hardened resins to fracture fill emeralds in the hope of providing a more permanent treatment to stones that require a lot of it. This is often undertaken before the cutting process to ensure that any rough stones that would normally have too many fractures and therefore be too structurally weak are able to survive the pressure of the cutting and polishing wheel. Emeralds that are treated in this way are considered low in quality and value.
Origins: Emeralds from across the globe
The Colombian emerald is unanimously regarded as the finest in the world. However, each emerald must be judged on its merits, and it would be unfair to suggest that a stone from one region is automatically superior to another. None the less, origin greatly effects the value of a stone.
Emeralds have only been found in fewer than 20 countries. Of these, a mere 11 are still capable of producing gem-quality stones. The overwhelming majority of the worlds emeralds come from Brazil, Colombia and Zambia. Pakistan, Afghanistan and Russia are producers as well. None of the other locations for emerald is of commercial importance. Isolated emeralds can be found in North Carolina, in Austria and in Norway but these have been uniformly of medium and poorer quality.
Columbia has been the source of the finest emeralds for more than 500 years. These fine emeralds have long been used as the yardstick by which others are judged. It is not unusual to hear an expert praising an emerald from some other region with the words: 'It is as good as a Colombian.’
This is because Colombian stones are blessed with near-perfect colour chemistry, thanks to the varying concentrations of chromium and vanadium and the absence or near absence of iron. This lack of iron means that a first-class Colombian emerald fluoresces in normal light.
In plain English, the color has more body and the green is more vibrant. Additionally, some Colombian emeralds contain microscopic inclusions that scatter the light as it travels through the gem, giving them a velvety richness. There is a unique liveliness in the best Colombian emeralds – a green fire – that is instantly recognizable and highly desirable.
What is considered the finest green is seen in stones from two specific mining areas in Columbia, Muzo and Chivor, is called ‘old mine’ green. Hundreds of years ago, the stones were pulled from the earth and sent all over the world by the Spaniards.
The best mines in Colombia were abandoned in 1895. It is said, very little of the recently mined material can compare in the depth of color to that of the “old mine’ stones.
From our archives: Striking Belle Epoque emerald and diamond ring. The emerald is estimated to be 2.5 carats and certified to be of Columbian origin with minor traditional treatment. The filigree setting is finely executed with two old European cut diamonds weight approximately 2.5 carats combined, surrounded by additional single cut stones. Circa 1910.
Emerald is also found in the state of Minas Gerais, Brazil. A rugged region worked largely by independent miner and small scale operations. The Brazilian stones do not have the peppery inclusions common to African emeralds. The material, however, is very opaque. Brazilian lapudaries are extremely skilled and are able to cut the material so that Brazilian stones are often well proportioned and quite attractive. A frequent problem however is that there are many open veins in Brazilian crystals. A stone with open veins is usually treated to improve its colour.
From GIA: A limited amount of emeralds have so far been produced from the Fazenda Bonfim region in Brazil’s Rio Grande do Norte State. The faceted stones shown here weigh 1.29–1.92 ct, and the cabochon weighs 3.89 ct. Photo by Robert Weldon.
Zambia is home to the largest working emerald mine in the world. The emerald mining area is in the Copper Belt region near Kitwe. Zambian emeralds are now considered among the finest modern origins. The source is quite young, and was discovered in the 1950’s but was not a significant source of material until the 1980’s. This origin is known for producing emeralds that are bluish green and darker in tone often with dark inclusions.
In 1832, in the Ural Mountains of Russia, a seam of emeralds was discovered. After the discovery, quite a few jewellery pieces were made containing Russian emeralds. The stones were somewhat light in color, but relatively free from inclusions. These Russian mines have now stopped yielding the purer emeralds, the material produced today being extremely opaque and generally uninteresting.
It takes many years of comparing shades of green to develop connoisseurship in emeralds. A stones value is dependant on so many factors that are not always obvious to the untrained eye, which is why it is important to obtain a certificate when purchasing colored stones. Many laboratories exist to give certifications to authenticate origin and treatments of gemstones. The labs use high tech equipment along with expert gemologists to offer their educated opinions on the details of gemstones. In the United States, the Gemological Institute of America (GIA) and the American Gemological Laboratory (AGL) are both very respected and commonly used for colored stone grading and certification. In Switzerland, the SSEF and Gübelin Laboratories offer certificates for colored stones and are considered authorities.
Zucker, Benjamin. A connoisseur’s Guide, Gems and Jewels, New York, Thames and Hudson Inc., 1984
Hardy, Joanna. Emerald: Twenty-One Centuries of Jeweled Opulence and Power, New York, Thames and Hudson Inc., 2016