Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.[Hurlbut, Cornelius S. Jr., and Kammerling, Robert C. (1991). Gemology, John Wiley & Sons, New York, p. 203, .] Beryl has a hardness of 7.5–8 on the Mohs scale.
Etymology
The word "emerald" is derived (via and ), from
Vulgar Latin:
esmaralda/esmaraldus, a variant of
Latin smaragdus, which was via (smáragdos; "green gem"). The Greek word may have a Semitic, Sanskrit or Persian origin.
According to
Webster's Dictionary the term emerald was first used in the 14th century.
Properties determining value
Emeralds, like all colored
, are graded using four basic parameters known as "the four
Cs":
color,
clarity, cut and
carat weight. Normally, in grading colored gemstones, color is by far the most important criterion. However, in the grading of emeralds, clarity is considered a close second. A fine emerald must possess not only a pure verdant green
hue as described below, but also a high degree of transparency to be considered a top gemstone.
[Wise, R. W. (2001) Secrets of the Gem Trade: the connoisseur's guide to precious gemstones. Brunswick House Press, p. 108, .]
This member of the beryl family ranks among the traditional "big four" precious gems along with , Ruby and .
In the 1960s, the American jewelry industry changed the definition of emerald to include the green vanadium-bearing beryl. As a result, vanadium emeralds purchased as emeralds in the United States are not recognized as such in the United Kingdom and Europe. In America, the distinction between traditional emeralds and the new vanadium kind is often reflected in the use of terms such as "Colombian emerald".[Read, Peter (2008) Gemmology, 3rd rev. ed., NAG Press, p. 218, .]
Color
In
gemology,
[ Grading Fancy-Color Diamonds . Gemological Institute of America] color is divided into three components:
hue,
saturation, and
lightness. Emeralds occur in hues ranging from yellow-green to blue-green, with the primary hue necessarily being green. Yellow and blue are the normal secondary hues found in emeralds. Only gems that are medium to dark in tone are considered emeralds; light-toned gems are known instead by the species name
Beryl. The finest emeralds are approximately 75% tone on a scale where 0% tone is colorless and 100% is opaque black. In addition, a fine emerald will be saturated and have a hue that is bright (vivid). Gray is the normal saturation modifier or mask found in emeralds; a grayish-green hue is a dull-green hue.
Clarity
Emeralds tend to have numerous inclusions and surface-breaking fissures. Unlike diamonds, where the
loupe standard (i.e., 10× magnification) is used to grade clarity, emeralds are graded by eye. Thus, if an emerald has no visible inclusions to the eye (assuming normal visual acuity) it is considered flawless. Stones that lack surface breaking fissures are extremely rare and therefore almost all emeralds are treated ("oiled", see below) to enhance the apparent clarity. The inclusions and fissures within an emerald are sometimes described as
jardin (French for
garden), because of their mossy appearance.
[ Emerald Quality Factors . Gemological Institute of America.] Imperfections are unique for each emerald and can be used to identify a particular stone. Eye-clean stones of a vivid primary green hue (as described above), with no more than 15% of any secondary hue or combination (either blue or yellow) of a medium-dark tone, command the highest prices.
The relative non-uniformity motivates the cutting of emeralds in
cabochon form, rather than faceted shapes. Faceted emeralds are most commonly given an oval cut, or the signature emerald cut, a rectangular cut with facets around the top edge.
Treatments
Most emeralds are oiled as part of the post-
lapidary process, in order to fill in surface-reaching cracks so that clarity and stability are improved.
Cedar oil, having a similar
refractive index, is often used in this widely adopted practice. Other liquids, including synthetic oils and polymers with refractive indexes close to that of emeralds, such as
Opticon, are also used. The least expensive emeralds are often treated with epoxy resins, which are effective for filling stones with many fractures.
These treatments are typically applied in a vacuum chamber under mild heat, to open the pores of the stone and allow the fracture-filling agent to be absorbed more effectively.
[Liccini, Mark. Understanding Emerald Enhancements and Treatments . International Gem Society] The U.S. Federal Trade Commission requires the disclosure of this treatment when an oil-treated emerald is sold.
The use of oil is traditional and largely accepted by the gem trade, although oil-treated emeralds are worth much less than untreated emeralds of similar quality. Untreated emeralds must also be accompanied by a certificate from a licensed, independent gemology laboratory. Other treatments, for example the use of green-tinted oil, are not acceptable in the trade.
Gems are graded on a four-step scale;
none,
minor,
moderate and
highly enhanced. These categories reflect levels of enhancement, not
clarity. A gem graded
none on the enhancement scale may still exhibit visible inclusions. Laboratories apply these criteria differently. Some gemologists consider the mere presence of oil or polymers to constitute enhancement. Others may ignore traces of oil if the presence of the material does not improve the look of the gemstone.
Emerald mines
Emeralds in antiquity were mined in
Ancient Egypt at locations on Mount Smaragdus since 1500 BC, and India and Austria since at least the 14th century AD.
The Egyptian mines were exploited on an industrial scale by the Roman and Byzantine Empires, and later by Islamic conquerors. Mining in Egypt ceased with the discovery of the Colombian deposits. Today, only ruins remain in Egypt.
["Romans organized the mines as a multinational business..." Finlay, Victoria. Jewels: A Secret History (Kindle Location 3098). Random House Publishing Group. Kindle Edition.]
Colombia is by far the world's largest producer of emeralds, constituting 50–95% of the world production, with the number depending on the year, source and grade.[Carrillo, V. (2001). Compilación y análisis de la información geológica referente a la explotación esmeraldífera en Colombia. Informe de contrato 124. INGEOMINAS] Emerald production in Colombia has increased drastically in the last decade, increasing by 78% from 2000 to 2010.[ Emerald Mining Areas in Colombia , with location map of these three districts.] Rare Trapiche emerald are found in Colombia, distinguished by ray-like spokes of dark impurities.
Zambia is the world's second biggest producer, with its Kafubu River area deposits (Kagem Mines) about southwest of Kitwe responsible for 20% of the world's production of gem-quality stones in 2004.[Behling, Steve and Wilson, Wendell E. (1 January 2010) " The Kagem emerald mine: Kafubu Area, Zambia", The Mineralogical Record ] In the first half of 2011, the Kagem Mines produced 3.74 tons of emeralds.
Emeralds are found all over the world in countries such as Afghanistan, Australia, Austria, Brazil,[" Maior esmeralda do mundo, encontrada no Brasil, será leiloada no Canadá ". UOL (18 January 2012)] Bulgaria, Cambodia, Canada, China, Egypt, Ethiopia, France, Germany, India, Kazakhstan, Madagascar, Mozambique, Namibia, Nigeria, Norway, Pakistan, Russia, Somalia, South Africa, Spain, Switzerland, Tanzania, the United States, Zambia, and Zimbabwe.[ Emeralds in the Yukon Territory . Yukon Geological Survey.]
Origin determinations
Since the onset of concerns regarding diamond origins, research has been conducted to determine if the mining location could be determined for an emerald already in circulation. Traditional research used qualitative guidelines such as an emerald's color, style and quality of cutting, type of fracture filling, and the anthropological origins of the artifacts bearing the mineral to determine the emerald's mine location. More recent studies using energy-dispersive X-ray spectroscopy methods have uncovered trace chemical element differences between emeralds, including ones mined in close proximity to one another. American gemologist David Cronin and his colleagues have extensively examined the chemical signatures of emeralds resulting from fluid dynamics and subtle precipitation mechanisms, and their research demonstrated the chemical homogeneity of emeralds from the same mining location and the statistical differences that exist between emeralds from different mining locations, including those between the three locations: Muzo, Coscuez, and Chivor, in Colombia, South America.
Synthetic emerald
Both hydrothermal and
flux method synthetics have been produced, and a method has been developed for producing an emerald overgrowth on colorless
beryl. The first commercially successful emerald synthesis process was that of
Carroll Chatham, likely involving a lithium vanadate flux process, as Chatham's emeralds do not have any water and contain traces of vanadate, molybdenum and vanadium.
The other large producer of flux emeralds was
Pierre Gilson Sr., whose products have been on the market since 1964. Gilson's emeralds are usually grown on natural colorless beryl seeds, which are coated on both sides. Growth occurs at the rate of 1 mm per month, a typical seven-month growth run produces emerald crystals 7 mm thick.
[Nassau, K. (1980) Gems Made By Man, Gemological Institute of America, .]
Hydrothermal synthetic emeralds have been attributed to IG Farben, Nacken, Tairus, and others, but the first satisfactory commercial product was that of Johann Lechleitner of Innsbruck, Austria, which appeared on the market in the 1960s. These stones were initially sold under the names "Emerita" and "Symeralds", and they were grown as a thin layer of emerald on top of natural colorless beryl stones. Later, from 1965 to 1970, the Linde Division of Union Carbide produced completely synthetic emeralds by hydrothermal synthesis. According to their patents (attributable to Edith Flanigen),[Geological Magazine "Hydrothermal process for growing crystals having the structure of beryl in an alkaline halide medium" Issue date: 2 March 1971] acidic conditions are essential to prevent the chromium (which is used as the colorant) from precipitating. Also, it is important that the silicon-containing nutrient be kept away from the other ingredients to prevent nucleation and confine growth to the seed crystals. Growth occurs by a diffusion-reaction process, assisted by convection. The largest producer of hydrothermal emeralds today is Tairus, which has succeeded in synthesizing emeralds with chemical composition similar to emeralds in alkaline deposits in Colombia, and whose products are thus known as “Colombian created emeralds” or “Tairus created emeralds”.[Hurlbut, Cornelius S. Jr. and Kammerling, Robert C. (1991) Gemology, John Wiley & Sons, New York, p. 81, .]
Synthetic emeralds are often referred to as "created", as their chemical and gemological composition is the same as their natural counterparts. The U.S. Federal Trade Commission (FTC) has very strict regulations as to what can and what cannot be called a "synthetic" stone. The FTC says: "§ 23.23(c) It is unfair or deceptive to use the word "laboratory-grown", "laboratory-created", "manufacturer-created", or "synthetic" with the name of any natural stone to describe any industry product unless such industry product has essentially the same optical, physical, and chemical properties as the stone named."
Historical and cultural references
-
Emerald is regarded as the traditional birthstone for May as well as the traditional gemstone for the astrological sign of Taurus.
-
Traditional alchemy ascribes several uses and characteristics to emeralds:
The virtue of the Emerald is to counteract poison. They say that if a venomous animal should look at it, it will become blinded. The gem also acts as a preservative against epilepsy; it cures leprosy, strengthens sight and memory, checks copulation, during which act it will break, if worn at the time on the finger.
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According to French writer Brantôme ( 1540–1614) Hernán Cortés had one of the emeralds which he had looted from Mexico engraved gem, Inter Natos Mulierum non surrexit major ("Among those born of woman there hath not arisen a greater," Matthew 11:11), in reference to John the Baptist. Brantôme considered engraving such a beautiful and simple product of nature sacrilegious and considered this act the cause for Cortez's loss in 1541 of an extremely precious pearl,
[To which he dedicated the work, A beautiful and incomparable pearl] and even for the death of King Charles IX of France, who died (1574) soon afterward.[Compare:
]
-
In American author L. Frank Baum's 1900 children's novel The Wonderful Wizard of Oz, and the 1939 MGM film adaptation, the protagonist must travel to an Emerald City to meet the eponymous character, the Wizard.
-
The chief deity of one of India's most famous temples, the Meenakshi Amman Temple in Madurai, is the goddess Minakshi, whose idol is traditionally thought to be made of emerald.
Notable emeralds
|
|
Chipembele | Zambia, 2021 | 7,525 carats (1.505 kg) | Israel Diamond Exchange, Eshed – Gemstar |
Bahia Emerald | Brazil, 2001 | 180,000 carats, crystals in host rock 752 lb (341 kg) | Los Angeles County Sheriff's Department |
Carolina Emperor | United States, 2009 | 310 carats uncut, 64.8 carats cut | North Carolina Museum of Natural Sciences, Raleigh |
| Chalk Emerald | Colombia | 38.40 carats cut, then recut to 37.82 carats | National Museum of Natural History, Washington |
| Duke of Devonshire Emerald | Colombia, before 1831 | 1,383.93 carats uncut | Natural History Museum, London |
Emerald of Saint Louis | Austria, probably Habachtal | 51.60 carats cut | National Museum of Natural History, Paris |
Gachalá Emerald | Colombia, 1967 | 858 carats uncut | National Museum of Natural History, Washington |
| Mogul Mughal Emerald | Colombia, 1107 A.H. (1695–1696 AD) | 217.80 carats cut | Museum of Islamic Art, Doha, Qatar |
Rockefeller Emerald | Colombia | 18.04 carats Octagonal step-cut | Private collection |
Patricia Emerald | Colombia, 1920 | 632 carats uncut, dihexagonal (12 sided) | American Museum of Natural History, New York |
Mim Emerald[Bouillard, J.-C. and Jeanne-Michaud, A. (2016) "101 minéraux et pierres précieuses – qu'il faut avoir vus dans sa vie". Hors collection, Dunod. .] | Colombia, 2014 | 1,390 carats uncut, dihexagonal (12 sided) | Mim Museum, Beirut |
Gallery
File:Émeraude, quartz 2.jpg|Emerald on quartz, from Carnaiba Mine, Pindobaçu, Campo Formoso ultramafic complex, Bahia, Brazil
File:Chalk emerald 03.jpg|The Chalk Emerald ring, containing a top-quality 37-carat emerald, in the U.S. National Museum of Natural History
File:Зүмірет.jpg|Emerald crystals
File:Beryl-130023.jpg|A 5-carat emerald from Muzo with hexagonal cross-section
File:Gachala Emerald 3526711557 849c4c7367.jpg|Gachalá Emerald, one of the largest gem emeralds in the world, at . Found in 1967 at La Vega de San Juan mine in Gachalá, Colombia. Housed at the National Museum of Natural History in Washington, D.C.
File:Béryl var. émeraude sur gangue (Muzo Mine Boyaca - Colombie) -2.jpg|Colombian emeralds
File:Rough emerald crystals from Panjshir Valley Afghanistan.jpg|Rough emerald crystals from Panjshir Valley Afghanistan
File:Mim emerald.jpg|Large, di-hexagonal prismatic crystal of 1,390 carats uncut with a deep green color. It is transparent and features few inclusions in the upper 2/3, and is translucent in the lower part. Housed at the Mim Museum, Beirut, Lebanon.
See also
Notes
Further reading
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Cooper, J. C. (ed.) (1992). Brewer's Myth and Legend. New York: Cassell Publishers Ltd. .
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Giuliani, Gaston, Ed. (2022). Émeraudes, tout un monde. Led Editions du Piat,
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Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York: John Wiley and Sons. .
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Sinkankas, John (1994). Emerald & Other Beryls. Prescott, Ariz.: Geoscience Press. .
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Tavernier, Jean-Baptiste (1925 1676). Travels in India (second edition), Volume II. Edited by William Crooke and translated by V. Ball. London: Oxford University Press.
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Weinstein, Michael (1958). The World of Jewel Stones. New York: Sheriden House. .
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Wise, Richard W. (2003). Secrets of the Gem Trade: The Connoisseur's Guide to Precious Gemstones. Lenox, Mass.: Brunswick House Press. . . Online Emerald chapters.
External links
