Difference between revisions of "Emerald" - New World Encyclopedia

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== Occurrence ==
 
== Occurrence ==
  
Emeralds in antiquity were mined by the people of [[Egypt]], [[Austria]], and the [[Swat]]* region of northern [[Pakistan]].<ref>Giuliani, Gaston, Marc Chaudisson, Henri-Jean Schubnel, Daniel-H. Piat, Claire Rollion-Bard, Christian France-Lanord, Didier Giard, Daniel de Narvaez, and Benjamin Rondeau (2000). “Oxygen Isotopes and Emerald Trade Routes Since Antiquity.” ''Science'', January 28, 2000, pp. 631-633.</ref> <ref>Giuliani, Gaston, Michèle Heuze, and Marc Chaudisson (2000b). “La route des emeraudes anciennes.” ''Pour la Science'', Nov. 2000, pp. 58-65.</ref>
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Emeralds in antiquity were mined by the people of [[Egypt]], [[Austria]], and northern [[Pakistan]].<ref>Giuliani, Gaston, Marc Chaudisson, Henri-Jean Schubnel, Daniel-H. Piat, Claire Rollion-Bard, Christian France-Lanord, Didier Giard, Daniel de Narvaez, and Benjamin Rondeau (2000). “Oxygen Isotopes and Emerald Trade Routes Since Antiquity.” ''Science'', January 28, 2000, pp. 631-633.</ref> <ref>Giuliani, Gaston, Michèle Heuze, and Marc Chaudisson (2000b). “La route des emeraudes anciennes.” ''Pour la Science'', Nov. 2000, pp. 58-65.</ref> A rare type of emerald known as a "trapiche emerald" is occasionally found in the mines of [[Colombia]]. A trapiche emerald exhibits a starlike pattern&mdash;it has rays of dark carbon impurities that give the emerald a six-pointed, radial pattern. It is named for the ''trapiche'', a grinding wheel used to process [[sugarcane]]* in the region. [http://micro.magnet.fsu.edu/birthstones/pages/emerald.html]
  
A rare type of emerald known as a "trapiche emerald" is occasionally found in the mines of [[Colombia]]. A trapiche emerald exhibits a starlike pattern&mdash;it has rays of dark carbon impurities that give the emerald a six-pointed, radial pattern. It is named for the ''trapiche'', a grinding wheel used to process [[sugarcane]]* in the region. [http://micro.magnet.fsu.edu/birthstones/pages/emerald.html]
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It is thought that the elemental constituents of emerald were brought together during such geological processes as orogenesis (mountain building), metamorphism, and land erosion. Later, crystals of the gemstones were formed. The flaws observed in an emerald are a result of the geological processes by which it was formed.
  
 
==Synthetic emeralds==
 
==Synthetic emeralds==

Revision as of 08:50, 18 January 2007

For other uses, see Emerald (disambiguation).
Emerald
Emerald specimen with matrix.jpg
Emerald with host rock
General
CategoryMineral
Chemical formulaBeryllium aluminum silicate with chromium, Be3Al2(SiO3)6::Cr
Identification
ColorGreen
Crystal habitHexagonal Crystals
Crystal systemHexagonal
CleavagePoor Basal Cleavage (Seldom Visible)
FractureConchoidal
Mohs Scale hardness7.5 - 8.0
LusterVitreous
Refractive index1.576 - 1.582
PleochroismDistinct, Blue-Green/Yellow-Green
StreakWhite
Specific gravity2.70 - 2.78

Emerald (from the Greek word smaragdos, through the French esmeralde, meaning "green gemstone") is a green variety of the mineral beryl and is among the most valuable gemstones in the world.

Characteristics

The mineral beryl consists of beryllium aluminum silicate (Be3Al2(SiO3)6), and the emerald variety is colored green by the presence of traces of chromium and vanadium, and sometimes iron. The color varies in shades of green and bluish green. In addition, emeralds come in a wide spectrum of clarity, along with various numbers of inclusions.[1]

The emerald has a hardness of about 7.5 on the 10-point Mohs scale of hardness. This hardness rating decreases, however, with an increase in the number of inclusions in the stone. Most emeralds have many inclusions, and it is rare to find an emerald with only minor inclusions. Consequently, the toughness (resistance to breakage) is generally rated as poor.

Most emeralds are oiled as part of the post-lapidary process. The amount of oil entering an emerald microfissure is roughly equivalent to the size of a period in print.

Occurrence

Emeralds in antiquity were mined by the people of Egypt, Austria, and northern Pakistan.[2] [3] A rare type of emerald known as a "trapiche emerald" is occasionally found in the mines of Colombia. A trapiche emerald exhibits a starlike pattern—it has rays of dark carbon impurities that give the emerald a six-pointed, radial pattern. It is named for the trapiche, a grinding wheel used to process sugarcane in the region. [1]

It is thought that the elemental constituents of emerald were brought together during such geological processes as orogenesis (mountain building), metamorphism, and land erosion. Later, crystals of the gemstones were formed. The flaws observed in an emerald are a result of the geological processes by which it was formed.

Synthetic emeralds

Emerald showing its hexagonal structure.

The rarity and value of emerald have provided the incentive for developing synthetic emeralds. Synthetics have been produced by "flux-growth" and "hydrothermal" processes, including a method for producing an emerald overgrowth on colorless beryl.

The first commercially successful process for synthetic emeralds was that of Carroll C. Chatham. Stones produced by this process do not contain water but have traces of molybdenum and vanadium, indicating that a lithium vanadate flux process was probably used. Pierre Gilson Sr. has been the other large producer of flux emeralds, which 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 millimeter (mm) per month, and a typical seven-month growth run produces emerald crystals with a thickness of 7 mm (Nassau, K., 1980, Gems Made by Man).

Hydrothermal synthetic emeralds have been attributed to IG-Farben, Nacken, Chatham, and others, but the first satisfactory commercial product was that of Johann Lechleitner of Inbruck, Austria. These stones, which appeared on the market in the 1960s, were initially sold under the names "Emerita" and "Symeralds" and were grown as a thin layer of emerald on top of natural, colorless beryl stones. Although not much is known about the original process, it is assumed that Lechleitner emeralds were grown in acidic conditions. Later, from 1965 to 1970, the Linde Division of Union Carbide produced completely synthetic emeralds by hydrothermal synthesis. According to their patents (US3,567,642 and US3,567,643), acidic conditions are essential to prevent chromium (the colorant) from precipitating. Typical growth conditions include pressures of 700-1400 bars at temperatures of 500 to 600 °C, with a temperature gradient of 10 to 25 °C. Growth rates as fast as 1/3 mm per day can be attained.

Flux-grown synthetic emeralds fluoresce a dull red when examined with long-wave ultraviolet light, because of an indicator added during the process of synthesis. Natural specimens, by contrast, do not fluoresce in this manner.

A synthetic emerald may be referred to as "created." Its chemical and gemological composition is exactly equivalent to that of its natural counterpart. The Federal Trade Commission (FTC) has strict regulations about what can and cannot be called "synthetic" stone. The FTC says: "... [created stone must have] essentially the same optical, physical, and chemical properties as the stone named."[2]

Furthermore, all natural emeralds (except for the red bixbite beryls of Utah, which are anhydrous) have water inclusions, as they are of hydrothermal origin. Likewise, hydrothermally grown synthetic emeralds contain water molecules. On the other hand, flux-grown synthetic emeralds contain no water. For this reason, flux-grown emeralds are more stable when subjected to high temperatures. In addition, wispy, veil-like inclusions are common in flux-grown synthetic emeralds.

Historical usage and trivia

The Gachala Emerald, at 858 carats, is one of the largest gem emeralds in the world. It was found in 1967 at the La Vega de San Juan mine in Gachalá, Colombia.
  • Emeralds have been highly valued since ancient times. For instance, the Aztecs and Incas of South America considered these gems holy. In addition, the Hindu scriptures known as the Vedas assert that emeralds promise good luck and enhance well-being.[4]
  • Emerald is regarded as the birthstone for April and May, as well as the traditional gemstone for the astrological sign of Taurus.
  • In some cultures, the emerald is the traditional gift for the 55th wedding anniversary. It is also used as a 20th and 35th wedding anniversary stone.
  • According to Rebbenu Bachya, the Hebrew word "Nofech" in Exodus 28:18 means "Emerald", and was the stone on the Ephod representing the tribe of Judah. According to other commentaries, however, "Nofech" means "garnet", and another stone, the "Bareqet", representing the tribe of Levi, is thought to be emerald.

Famous emeralds

  • Gachala Emerald (origin: Colombia)
  • Chalk Emerald (origin: Colombia)
  • Duke of Devonshire Emerald (origin: Colombia)
  • Mackay Emerald

See also

Footnotes

  1. In mineralogy, an "inclusion" is any material trapped within a mineral during its formation.
  2. Giuliani, Gaston, Marc Chaudisson, Henri-Jean Schubnel, Daniel-H. Piat, Claire Rollion-Bard, Christian France-Lanord, Didier Giard, Daniel de Narvaez, and Benjamin Rondeau (2000). “Oxygen Isotopes and Emerald Trade Routes Since Antiquity.” Science, January 28, 2000, pp. 631-633.
  3. Giuliani, Gaston, Michèle Heuze, and Marc Chaudisson (2000b). “La route des emeraudes anciennes.” Pour la Science, Nov. 2000, pp. 58-65.
  4. Emerald, "Gem by Gem" series, International Colored Gemstone Association.

References
ISBN links support NWE through referral fees

  • Cooper, J.C. (Ed.) (1992). Brewer's Myth and Legend. New York: Cassell Publishers Ltd. ISBN 0-304-34084-7.
  • Sinkankas, John (1994). Emerald & Other Beryls. Tucson, AZ: Geoscience Press. ISBN 0-8019-7114-4.
  • Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York: John Wiley and Sons. ISBN 0-471-80580-7.
  • Nassau, Kurt (1980). Gems made by man. Carlsbad, CA: Gemological Institute of America. ISBN 0873110161 (ISBN-13: 978-0873110167).
  • Weinstein, Michael (1967). The World of Jewel Stones. New York, NY: Sheridan House. ASIN: B000IN1RC4.
  • Emerald "Gem by Gem" series. International Colored Gemstone Association. Retrieved January 17, 2007.

External links

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