Emerald

Emerald is a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium and sometimes vanadium.[2] Beryl has a hardness of 7.5–8 on the 10 point Mohs scale of mineral hardness.[2] Most emeralds are highly included, so their toughness (resistance to breakag
The word "Emerald" is derived (via Old French: Esmeraude and Middle English: Emeraude), from Vulgar Latin: Esmaralda/Esmaraldus, a variant of Latin Smaragdus, which originated in Greek: σμάραγδος (smaragdos; "green gem"); its original source being either the Hebrew word אזמרגד izmargad meaning "emerald" or "green"[3] or the Sanskrit word मरकत marakata meaning "emerald." The name could also be related to the Semitic word baraq (בָּרָק ;البُراق; "lightning" or "shine") (cf. Hebrew: ברקת bareqeth and Arabic: برق barq "lightning"). It is the same source for the names Persian (زمرّد zomorrod), Turkish (zümrüt), Sanskrit (मरकत ; marakata), Kannada (ಪಚ್ಚೆ ; Pacche), Telugu (Paccha), Georgian (ზურმუხტი; zurmukhti), Russian (изумруд; izumrud)[4] and Armenian zmruxt.
==[edit] Properties determining value==
Cut emeraldsEmeralds, like all colored gemstones, are graded using four basic parameters – the four Cs of Connoisseurship: Color, Cut, Clarity and Crystal. The last C, crystal is simply used as a synonym that begins with C for transparency or what gemologists call diaphaneity. Before the 20th century, jewelers used the term water as in "a gem of the finest water"[5] to express the combination of two qualities, color and crystal. Normally, in the grading of colored gemstones, color is by far the most important criterion. However, in the grading of emerald, crystal is considered a close second. Both are necessary conditions. 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 gem.[6]
In the 1960s the American jewelry industry changed the definition of 'emerald' to include the green vanadium-bearing beryl as emerald. As a result, vanadium emeralds purchased as emeralds in the United States are not recognized as such in the UK 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.'[7]
===[edit] Color===
Scientifically speaking, 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, blue, and red — the hues found adjacent to green on the spectral color wheel — are the normal secondary hues found in emeralds. Only gems that are medium to dark in tone are considered emerald; light-toned gems are known instead by the species name green beryl. In addition, the hue of an emerald must be bright (vivid). Gray is the normal saturation modifier or mask found in emerald; a grayish-green hue is a dull green.
===[edit] Clarity===
Emerald tends to have numerous inclusions and surface breaking fissures. Unlike diamond, where the loupe standard, i.e. 10X magnification, is used to grade clarity, emerald is 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", to enhance the apparent clarity. 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.[6] This relative crystal non-uniformity makes emeralds more likely than other gemstones to be cut into cabochons, rather than faceted shapes.
===[edit] Treatments===
Most emeralds are oiled as part of the post lapidary process, in order to improve their clarity. Cedar oil, having a similar refractive index, is often used in this generally accepted practice. Other liquids, including synthetic oils and polymers with refractive indexes close to that of emerald such as Opticon are also used. The U.S. Federal Trade Commission requires the disclosure of this treatment when a treated emerald is sold.[8] The use of oil is traditional and largely accepted by the gem trade. Other treatments, for example the use of green-tinted oil, are not acceptable in the trade. The laboratory community has recently standardized the language for grading the clarity of emeralds. Gems are graded on a four step scale; none, minor, moderate and highly enhanced. Note that these categories reflect levels of enhancement not clarity. A gem graded none on the enhancement scale may still exhibit visible inclusions. Laboratories tend to apply these criteria differently. Some gem labs 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 materially improve the look of the gemstone.
Given that the vast majority of all emeralds are treated as described above, and the fact that two stones that appear visually similar may actually be quite far apart in treatment level and therefore in value, a consumer considering a purchase of an expensive emerald is well advised to insist upon a treatment report from a reputable gemological laboratory. All other factors being equal, a high quality emerald with an enhancement level of moderate should cost half an identical stone graded none.[9]e) is classified as generally poor.
References
http://en.wikipedia.org/wiki/Emerald
Category:Not Related to Almandine 2018
Category:Almandine 2018