Editing Emerald (section)

== Properties determining value ==
[[File:5 Emeralds from Colombia.JPG|thumb|left|Cut emeralds]]

Emeralds, like all colored [[gemstone]]s, are graded using four basic parameters known as "the four ''C''s": ''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 and translucency|transparency]] to be considered a top gemstone.<ref name=Wise>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}}.</ref>

This member of the beryl family ranks among the traditional "big four" precious gems along with [[diamond]]s, [[Ruby|rubies]] and [[sapphire]]s.<ref>{{Cite web|title=Emerald Value, Price, and Jewelry Information|url=https://www.gemsociety.org/article/emerald-jewelry-and-gemstone-information/|access-date=16 November 2021|website=International Gem Society|language=en|archive-date=16 November 2021|archive-url=https://web.archive.org/web/20211116082504/https://www.gemsociety.org/article/emerald-jewelry-and-gemstone-information/|url-status=live}}</ref>

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".<ref name=Read>Read, Peter (2008) ''Gemmology'', 3rd rev. ed., NAG Press, p. 218, {{ISBN|0719803616}}.</ref>

=== Color ===

In [[gemology]],<ref>[http://gia4cs.gia.edu/EN-US/gr-colored-diamonds-gemstones.htm Grading Fancy-Color Diamonds] {{webarchive|url=https://web.archive.org/web/20141102115539/http://gia4cs.gia.edu/en-us/gr-colored-diamonds-gemstones.htm |date=2 November 2014 }}. Gemological Institute of America</ref> color is divided into three components: ''[[hue]]'', ''[[Saturation (color theory)|saturation]]'', and ''[[lightness|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 ''[[Beryl|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.<ref name=Wise />

=== Clarity ===
[[File:Emerald in a quartz and pegmatite matrix.JPG|thumb|Brazilian emerald (grass-green variety of the mineral beryl) in a quartz-pegmatite matrix with typical hexagonal, prismatic crystals.<ref>Bonewitz, R. (2005). ''Rock and gem''. New York: DK Pub. pp. 292–293. {{ISBN|0756633427}}.</ref>]]
Emeralds tend to have numerous inclusions and surface-breaking [[Cleavage (crystal)|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 [[inclusion (mineral)|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.<ref>[http://www.gia.edu/emerald-quality-factor Emerald Quality Factors] {{webarchive|url=https://web.archive.org/web/20140223032811/http://www.gia.edu/emerald-quality-factor |date=23 February 2014 }}. Gemological Institute of America.</ref> 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.<ref name=Wise /> 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.<ref>{{Cite journal|date=1991|title=Gems & Gemology|url=https://www.gia.edu/doc/SU91.pdf|journal=Gems & Gemology|volume=XXVII|access-date=19 May 2021|archive-date=19 May 2021|archive-url=https://web.archive.org/web/20210519013713/https://www.gia.edu/doc/SU91.pdf|url-status=live}}</ref><ref>{{Cite journal|date=2001|title=Emerald Treatments|url=https://www.ssef.ch/wp-content/uploads/2018/03/2001_Kiefert_Emerald_treatments.pdf|journal=Kiefert|access-date=19 May 2021|archive-date=19 May 2021|archive-url=https://web.archive.org/web/20210519013714/https://www.ssef.ch/wp-content/uploads/2018/03/2001_Kiefert_Emerald_treatments.pdf|url-status=live}}</ref> 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.<ref>Liccini, Mark. [http://www.gemsociety.org/article/emerald-enhancement/ Understanding Emerald Enhancements and Treatments] {{webarchive|url=https://web.archive.org/web/20141221144224/http://www.gemsociety.org/article/emerald-enhancement/ |date=21 December 2014 }}. International Gem Society</ref> The U.S. [[Federal Trade Commission]] requires the disclosure of this treatment when an oil-treated emerald is sold.<ref name=ftc /> 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.<ref>{{cite book|last1=Read|first1=P. G.|title=Gemmology|publisher=Elsevier|isbn=978-1-4831-4467-2|page=180|url=https://books.google.com/books?id=b-7fBAAAQBAJ&q=oil+enhancement+emerald|access-date=30 March 2017|language=en|url-status=live|archive-url=https://web.archive.org/web/20170331024513/https://books.google.com.au/books?id=b-7fBAAAQBAJ&dq=oil+enhancement+emerald&source=gbs_navlinks_s|archive-date=31 March 2017|date=22 October 2013}}</ref> 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.<ref>{{cite book|last1=Matlins|first1=Antoinette Leonard|last2=Bonanno|first2=Antonio C.|title=Jewelry & Gems, the Buying Guide: How to Buy Diamonds, Pearls, Colored Gemstones, Gold & Jewelry with Confidence and Knowledge|publisher=Gemstone Press|isbn=978-0-943763-71-2|page=126|url=https://books.google.com/books?id=WUBWz22wRtEC&q=gemstone+enhancement+traces+of+oil&pg=PA126|access-date=30 March 2017|language=en|url-status=live|archive-url=https://web.archive.org/web/20170330180745/https://books.google.com.au/books?id=WUBWz22wRtEC&pg=PA126&dq=gemstone+enhancement+traces+of+oil&hl=en&sa=X&ved=0ahUKEwj8ruzuuv3SAhUT3mMKHXM_CdwQ6AEILTAD#v=onepage&q=gemstone%20enhancement%20traces%20of%20oil&f=false|archive-date=30 March 2017|year=2009}}</ref>