Emerald is a gemstone, and 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 breakage) is classified as generally poor.
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").
Emeralds, 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 a synonym for transparency, or what gemologists call diaphaneity. Before the 20th century, jewelers used the term water, as in "a gem of the finest water,"[3]
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 emeralds, 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.[4]
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.'[5]
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 and blue 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. The finest emerald are approximately
75% tone on a scale where 0% tone would be colorless and 100% would be
opaque black. In addition, a fine stone should be well saturated; the
hue of an emerald should be bright (vivid). Gray is the normal
saturation modifier or mask found in emerald; a grayish-green hue is a
dull green hue.[4]
Emeralds are green by definition (the name is derived from the Greek word 'smaragdus', meaning green).[6] Emeralds are the green variety of beryl, a mineral which comes in many other colors that are sometimes also used as gems, such as blue aquamarine, yellow heliodor, pink morganite and colorless goshenite.[7]
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.[4] This relative crystal non-uniformity makes emeralds more likely than other gemstones to be cut into cabochons, rather than faceted shapes.
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
moderate enhancement should cost half the price of an identical stone
graded none.
Emerald localities
Emeralds in antiquity[when?] were mined in Egypt, India, and Austria. 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.[10][11][12][13] Emerald production in Colombia has increased drastically in the last decade, increasing by 78% from 2000 to 2010.[14] The three main emerald mining areas in Colombia are Muzo, Coscuez, and Chivor.[15] Rare 'trapiche' emeralds are found in Colombia, distinguished by a six-pointed radial pattern made of ray-like spokes of dark carbon impurities.
Zambia
is the world's second biggest producer, with its Kafubu River area
deposits (Kagem Mines) about 45 km southwest of Kitwe responsible for
20% of the world's production of gem quality stones in 2004.[16] In the first half of 2011 the Kagem mines produced 3.74 tons of emeralds.[17] Zambian emeralds are of very high quality, being less porous and brittle than Colombian emeralds, with more even color.
Emeralds are found all over the world in countries such as Afghanistan, Australia, Austria, Brazil,[18] Bulgaria, Cambodia, Canada, China, Egypt, Ethiopia, France, Germany, India, Italy, Kazakhstan, Madagascar, Mozambique, Namibia, Nigeria, Norway, Pakistan, Russia, Somalia, South Africa, Spain, Switzerland, Tanzania, United States, Zambia, and Zimbabwe.[1] In the US, emeralds have been found in Connecticut, Montana, Nevada, North Carolina, and South Carolina.[1] In 1997 emeralds were discovered in the Yukon.[19]
