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Emerald

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For other uses, see Emerald (disambiguation).

Emerald
Emerald crystal from Muzo, Colombia
General
CategoryBeryl variety
Formula
(repeating unit)		Be3Al2(SiO3)6
Crystal systemHexagonal (6/m 2/m 2/m) Space group: P6/mсc
Space group(6/m 2/m 2/m) – dihexagonal dipyramidal
Unit cella = 9.21 Å, c = 9.19 Å; Z = 2
Identification
Formula mass537.50
ColorBluish green to green
Crystal habitMassive to well Crystalline
CleavageImperfect on the [0001]
FractureConchoidal
Mohs scale hardness7.5–8
LusterVitreous
StreakWhite
DiaphaneityTransparent to opaque
Specific gravityAverage 2.76
Optical propertiesUniaxial (−)
Refractive indexnω = 1.564–1.595,
nε = 1.568–1.602
Birefringenceδ = 0.0040–0.0070
Ultraviolet fluorescenceNone (some fracture-filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not)
References[1]
Main emerald producing countries

Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.[2] Beryl has a hardness of 7.5–8 on the Mohs scale.[2] Most emeralds have many inclusions,[3] so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.

Etymology

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The word "emerald" is derived (via Old French: esmeraude and Middle English: emeraude), from Vulgar Latin: esmaralda/esmaraldus, a variant of Latin smaragdus, which was via Ancient Greek: σμάραγδος (smáragdos; "green gem"). The Greek word may have a Semitic, Sanskrit or Persian origin.[4][5][6] According to Webster's Dictionary the term emerald was first used in the 14th century.[7]

Properties determining value

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Cut emeralds

Emeralds, like all colored gemstones, 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.[8]

This member of the beryl family ranks among the traditional "big four" gems along with diamonds, rubies and sapphires.[9]

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".[10]

Color

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In gemology,[11] color is divided into three components: hue, saturation, and tone. 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 green 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.[8]

Clarity

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Brazilian emerald (grass-green variety of the mineral beryl) in a quartz-pegmatite matrix with typical hexagonal, prismatic crystals.[12]

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.[13] 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.[8] 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

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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.[14][15] 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.[16] The U.S. Federal Trade Commission requires the disclosure of this treatment when an oil-treated emerald is sold.[17] 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.[18] 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.[19]

Emerald mines

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A Colombian trapiche emerald

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.[20] 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.[21]

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.[22][23][24][25] Emerald production in Colombia has increased drastically in the last decade, increasing by 78% from 2000 to 2010.[26] The three main emerald mining areas in Colombia are Muzo, Coscuez, and Chivor.[27] Rare "trapiche" emeralds 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 45 km (28 mi) southwest of Kitwe responsible for 20% of the world's production of gem-quality stones in 2004.[28] In the first half of 2011, the Kagem Mines produced 3.74 tons of emeralds.[29]

Emeralds are found all over the world in countries such as Afghanistan, Australia, Austria, Brazil,[30] 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.[1] In the US, emeralds have been found in Connecticut, Montana, Nevada, North Carolina, and South Carolina.[1] In 1998, emeralds were discovered in the Yukon Territory of Canada.[31]

Origin determinations

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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.[32]

Synthetic emerald

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Emerald showing its hexagonal structure

Both hydrothermal and flux-growth 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.[33] 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.[34]

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 E.M. Flanigen),[35] 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”.[36] Luminescence in ultraviolet light is considered a supplementary test when making a natural versus synthetic determination, as many, but not all, natural emeralds are inert to ultraviolet light. Many synthetics are also UV inert.[37]

Emerald made by hydrothermal synthesis

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 name]-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."[17]

Historical and cultural references

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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.[39]

Notable emeralds

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Emerald Origin Size Location
Chipembele[43] Zambia, 2021 7,525 carats (1.505 kg) Israel Diamond Exchange, Eshed – Gemstar[44]
Bahia Emerald[45] Brazil, 2001 180,000 carats, crystals in host rock 752 lb (341 kg) Los Angeles County Sheriff's Department[46]
Carolina Emperor[47][48] 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[49] Austria, probably Habachtal 51.60 carats cut National Museum of Natural History, Paris
Gachalá Emerald[50] 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 [51] Colombia 18.04 carats Octagonal step-cut Private collection
Patricia Emerald[52] Colombia, 1920 632 carats uncut, dihexagonal (12 sided) American Museum of Natural History, New York
Mim Emerald[53] Colombia, 2014 1,390 carats uncut, dihexagonal (12 sided) Mim Museum, Beirut
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  • Emerald on quartz, from Carnaiba Mine, Pindobaçu, Campo Formoso ultramafic complex, Bahia, Brazil
    Emerald on quartz, from Carnaiba Mine, Pindobaçu, Campo Formoso ultramafic complex, Bahia, Brazil
  • The Chalk Emerald ring, containing a top-quality 37-carat emerald, in the U.S. National Museum of Natural History
    The Chalk Emerald ring, containing a top-quality 37-carat emerald, in the U.S. National Museum of Natural History
  • Emerald crystals
    Emerald crystals
  • A 5-carat emerald from Muzo with hexagonal cross-section
    A 5-carat emerald from Muzo with hexagonal cross-section
  • Gachalá Emerald, one of the largest gem emeralds in the world, at 858 carats (171.6 g). 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.
    Gachalá Emerald, one of the largest gem emeralds in the world, at 858 carats (171.6 g). 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.
  • Colombian emeralds
    Colombian emeralds
  • Rough emerald crystals from Panjshir Valley Afghanistan
    Rough emerald crystals from Panjshir Valley Afghanistan
  • 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.
    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

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Notes

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  1. ^ To which he dedicated the work, A beautiful and incomparable pearl[citation needed]

References

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  1. ^ a b c "Emerald at Mindat". Mindat.org. 19 July 2010. Archived from the original on 12 July 2010. Retrieved 30 July 2010.
  2. ^ a b Hurlbut, Cornelius S. Jr., and Kammerling, Robert C. (1991). Gemology, John Wiley & Sons, New York, p. 203, ISBN 0-471-52667-3.
  3. ^ "Emerald Quality Factors". Gemological Institute of America. Archived from the original on 2 November 2016. Retrieved 1 November 2016.
  4. ^ "Definition of 'emerald'". Collins Dictionary. Retrieved 29 April 2024.
  5. ^ "smaragdus NOUN". Oxford English Dictionary. Retrieved 29 April 2024.
  6. ^ Harper, Douglas. "emerald". Online Etymology Dictionary.
  7. ^ "Definition of EMERALD". www.merriam-webster.com. Archived from the original on 25 September 2021. Retrieved 25 September 2021.
  8. ^ a b c Wise, R. W. (2001) Secrets of the Gem Trade: the connoisseur's guide to precious gemstones. Brunswick House Press, p. 108, ISBN 0-9728223-8-0.
  9. ^ "Emerald Value, Price, and Jewelry Information". International Gem Society. Archived from the original on 16 November 2021. Retrieved 16 November 2021.
  10. ^ Read, Peter (2008) Gemmology, 3rd rev. ed., NAG Press, p. 218, ISBN 0719803616.
  11. ^ Grading Fancy-Color Diamonds Archived 2 November 2014 at the Wayback Machine. Gemological Institute of America
  12. ^ Bonewitz, R. (2005). Rock and gem. New York: DK Pub. pp. 292–293. ISBN 0756633427.
  13. ^ Emerald Quality Factors Archived 23 February 2014 at the Wayback Machine. Gemological Institute of America.
  14. ^ "Gems & Gemology" (PDF). Gems & Gemology. XXVII. 1991. Archived (PDF) from the original on 19 May 2021. Retrieved 19 May 2021.
  15. ^ "Emerald Treatments" (PDF). Kiefert. 2001. Archived (PDF) from the original on 19 May 2021. Retrieved 19 May 2021.
  16. ^ Liccini, Mark. Understanding Emerald Enhancements and Treatments Archived 21 December 2014 at the Wayback Machine. International Gem Society
  17. ^ a b "Guides for the Jewelry, Precious Metals, and Pewter Industries". U.S. Federal Trade Commission. 30 May 1996. Archived from the original on 7 September 2008. Retrieved 30 July 2010.
  18. ^ Read, P. G. (22 October 2013). Gemmology. Elsevier. p. 180. ISBN 978-1-4831-4467-2. Archived from the original on 31 March 2017. Retrieved 30 March 2017.
  19. ^ Matlins, Antoinette Leonard; Bonanno, Antonio C. (2009). Jewelry & Gems, the Buying Guide: How to Buy Diamonds, Pearls, Colored Gemstones, Gold & Jewelry with Confidence and Knowledge. Gemstone Press. p. 126. ISBN 978-0-943763-71-2. Archived from the original on 30 March 2017. Retrieved 30 March 2017.
  20. ^ Giuliani G, Chaussidon M, Schubnel HJ, Piat DH, Rollion-Bard C, France-Lanord C, Giard D, de Narvaez D, Rondeau B (2000). "Oxygen Isotopes and Emerald Trade Routes Since Antiquity" (PDF). Science. 287 (5453): 631–3. Bibcode:2000Sci...287..631G. doi:10.1126/science.287.5453.631. PMID 10649992. Archived (PDF) from the original on 7 August 2011.
  21. ^ "Romans organized the mines as a multinational business..." Finlay, Victoria. Jewels: A Secret History (Kindle Location 3098). Random House Publishing Group. Kindle Edition.
  22. ^ Badawy, Manuela (13 June 2012). "Emeralds seek the 'De Beers' treatment". Reuters. Archived from the original on 5 August 2012. Retrieved 14 June 2012.
  23. ^ Dydyński, Krzysztof (2003). Colombia. Lonely Planet. p. 21. ISBN 0-86442-674-7.
  24. ^ Branquet, Y. Laumenier, B. Cheilletz, A. & Giuliani, G. (1999). "Emeralds in the Eastern Cordillera of Colombia. Two tectonic settings for one mineralization" (PDF). Geology. 27 (7): 597–600. Bibcode:1999Geo....27..597B. doi:10.1130/0091-7613(1999)027<0597:EITECO>2.3.CO;2. S2CID 55974313. Archived from the original (PDF) on 21 February 2019.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  25. ^ Carrillo, V. (2001). Compilación y análisis de la información geológica referente a la explotación esmeraldífera en Colombia. Informe de contrato 124. INGEOMINAS
  26. ^ Wacaster, Susan (March 2012). "2010 Minerals Yearbook: Colombia [ADVANCE RELEASE]" (PDF). United States Geological Survey. Archived (PDF) from the original on 13 August 2012. Retrieved 7 August 2012.
  27. ^ Emerald Mining Areas in Colombia Archived 29 September 2010 at the Wayback Machine, with location map of these three districts.
  28. ^ Behling, Steve and Wilson, Wendell E. (1 January 2010) "The Kagem emerald mine: Kafubu Area, Zambia", The Mineralogical Record Archived 10 May 2013 at the Wayback Machine
  29. ^ "What is Kagem Zambian Emerald?". Sharon Gulezian Jewelry. Retrieved 19 May 2021.
  30. ^ "Maior esmeralda do mundo, encontrada no Brasil, será leiloada no Canadá Archived April 7, 2014, at the Wayback Machine". UOL (18 January 2012)
  31. ^ Emeralds in the Yukon Territory Archived 31 March 2014 at the Wayback Machine. Yukon Geological Survey.
  32. ^ Cronin, David; Rendle, Andy (2012). "Determining the geographical origins of natural emeralds through nondestructive chemical fingerprinting". Journal of Gemmology. 33: 1–13. doi:10.15506/JoG.2012.33.1.1. Archived from the original on 17 November 2015.
  33. ^ O'Donoghue, Michael (1988). Gemstones. Dordrecht: Springer Netherlands. p. 310. ISBN 9789400911918. Archived from the original on 30 March 2017.
  34. ^ Nassau, K. (1980) Gems Made By Man, Gemological Institute of America, ISBN 0-87311-016-1.
  35. ^ Geological Magazine "Hydrothermal process for growing crystals having the structure of beryl in an alkaline halide medium" U.S. patent 3,567,642 Issue date: 2 March 1971
  36. ^ Schmetzer, Karl; Schwartz, Dietmar; Bernhardt, Heinz-Jurgen; Tobias Hager (2006–2007). "A new type of Tairus hydrothermally-grown synthetic emerald, colored by vanadium and copper" (PDF). Journal of Gemmology of Gemmological Association of Great Britain. 30 (1–2): 59–74. Archived from the original (PDF) on 11 July 2011.
  37. ^ Hurlbut, Cornelius S. Jr. and Kammerling, Robert C. (1991) Gemology, John Wiley & Sons, New York, p. 81, ISBN 0-471-52667-3.
  38. ^ Morgan, Diane (2007). From Satan's crown to the holy grail : emeralds in myth, magic, and history. Westport, Conn. [u.a.]: Praeger. p. 171. ISBN 978-0-275-99123-4. Archived from the original on March 30, 2017. Retrieved March 30, 2017.
  39. ^ Ruland, Martin (26 May 2014) [1612]. "Smaragdus". A Lexicon of Alchemy [Lexicon alchemia]. Translated by Waite, Arthur Edward. Altenmünster, Bavaria: Jazzybee Verlag (published 2014). ISBN 978-3-8496-4439-0. Archived from the original on 25 June 2022. Retrieved 25 June 2022. 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, it worn at the time on the finger.
  40. ^ Compare: de Bourdeill, Pierre (1864). Lalanne, Ludovic (ed.). Oeuvres complètes de Pierre de Bourdeille, seigneur de Brantome publièes d'après les manuscrits avec variantes et fragments inédits pour la Société de l'histoire de France (in French). Vol. 1: Grand Capitaines Estrangers. Paris: Jules Renouard. p. 52. Archived from the original on 25 June 2022. Retrieved 25 June 2022. [...] la belle et incomparable perle de cet Hernand Cortez, qu'il rapporta des Indes, sur laquelle il fit graver ces mots: Inter natos mulierum non surrexit major, [...] laquelle il perdit depuis devant Alger [...]. [...] Brantôme s'est trompé ici: le joyau dont il parle n'était point une perle, mais une émaraude.
  41. ^ Kunz, George Frederick (1915). Magic of Jewels and Charms. Philadelphia: Lippincott Company. pp. 305–306. ISBN 0-7661-4322-8. Archived from the original on October 17, 2012.
  42. ^ "Meenakshi Temple – Meenakshi Temple of Madurai, Meenakshi Amman Temple Madurai India". www.madurai.org.uk. Archived from the original on March 17, 2016. Retrieved January 18, 2016.
  43. ^ "Gemfields finds largest emerald ever at Zambia mine". MINING.COM. 8 November 2021. Archived from the original on 9 December 2021. Retrieved 9 December 2021.
  44. ^ Addow, Amina (2 November 2022). "World's largest uncut emerald weighs hefty 1.5 kg". Guinness World Records Limited. Archived from the original on 13 October 2023. Retrieved 15 October 2023.
  45. ^ Allen, Nick (24 September 2010). "Judge to decide who owns 250 million Bahia emerald.html". The Daily Telegraph, UK. Archived from the original on 28 September 2010. Retrieved 31 December 2010.
  46. ^ "The Curse of the Bahia Emerald, a Giant Green Rock That Ruins Lives". Wired. wired.com. Archived from the original on 15 December 2018. Retrieved 17 December 2018.
  47. ^ Gast, Phil (1 September 2010). "North Carolina emerald: Big, green and very rare". CNN. Cable News Network (Turner Broadcasting System, Inc.). Archived from the original on 25 September 2013. Retrieved 8 October 2013.
  48. ^ Stancill, Jane (16 March 2012). "N.C. gems to shine at museum". The News & Observer. The News & Observer Publishing Co. Archived from the original on 27 March 2012. Retrieved 8 October 2013.
  49. ^ "Emeraude de Saint Louis – St Louis Emerald". CRPG: Le Centre de Recherches Pétrographiques et Géochimiques. Archived from the original on March 4, 2016. Retrieved February 8, 2017.
  50. ^ "Gachala Emerald". National Museum of Natural History. Smithsonian Institution. 2017. Archived from the original on February 11, 2017. Retrieved February 8, 2017.
  51. ^ "10 jewels that made history". Christies. Archived from the original on 16 March 2020. Retrieved 22 December 2019.
  52. ^ "Patricia Emerald". AMNH. Archived from the original on September 5, 2015. Retrieved August 22, 2015.
  53. ^ Bouillard, J.-C. and Jeanne-Michaud, A. (2016) "101 minéraux et pierres précieuses – qu'il faut avoir vus dans sa vie". Hors collection, Dunod. ISBN 2100742272.

Further reading

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