Emerald is a gemstone and a variety of the mineral beryl6) colored green by trace amounts
of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the 10-point
Mohs scale of mineral hardness. Most emeralds are highly included, so their toughness is
classified as generally poor.
Etymology The word "Emerald" is derived, from Vulgar
Latin: Esmaralda/Esmaraldus, a variant of Latin Smaragdus, which originated in Greek:
σμάραγδος. Properties determining value
Emeralds, like all colored gemstones, are graded using four basic parameters–the four
Cs of Connoisseurship: Color, Cut, Clarity and Carat weight. Before the 20th century,
jewelers used the term water, as in "a gem of the finest water", to express the combination
of two qualities: color and clarity. Normally, in the grading of colored gemstones, color
is by far the most important criterion. However, in the grading of emeralds, clarity 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. 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".
Color In gemology, 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. Gray
is the normal saturation modifier or mask found in emerald; a grayish-green hue is a
dull green hue. Emeralds are green by definition. 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,
red red beryl or bixbite, not to be confused with bixbyite, and colorless goshenite.
Clarity Emerald tends to have numerous inclusions
and surface breaking fissures. Unlike diamond, where the loupe standard, i.e. 10× magnification,
is used to grade clarity, emerald is graded by eye. Thus, if an emerald has no visible
inclusions to the eye it is considered flawless. Stones that lack surface breaking fissures
are extremely rare and therefore almost all emeralds are treated to enhance the apparent
clarity. The inclusions and fissures within an emerald are sometime described as 'the
garden', because of their mossy appearance. These imperfections within the stone are unique
to each emerald and can be used to identify a particular stone. Eye-clean stones of a
vivid primary green hue with no more than 15% of any secondary hue or combination of
a medium-dark tone command the highest prices. This relative crystal non-uniformity makes
emeralds more likely than other gemstones to be cut into cabochons, rather than faceted
shapes. Faceted Emeralds are most commonly given the 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, improving their clarity and stability.
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 an oil treated emerald is sold. The use of oil is
traditional and largely accepted by the gem trade, although oil treated emeralds are worth
much less than un-treated emeralds of similar quality. Other treatments, for example the
use of green-tinted oil, are not acceptable in the trade. 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 severely less than an identical stone graded
none. Emerald localities
Emeralds in antiquity have been mined in Egypt since 1500 BCE, and India, and Austria since
at least the 14th century CE. 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. Emerald production in Colombia has increased drastically in the
last decade, increasing by 78% from 2000 to 2010. The three main emerald mining areas
in Colombia are Muzo, Coscuez, and Chivor. 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 about
45 km southwest of Kitwe responsible for 20% of the world's production of gem quality
stones in 2004. In the first half of 2011 the Kagem mines produced 3.74 tons of emeralds.
Emeralds are found all over the world in countries such as Afghanistan, Australia, Austria, Brazil,
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. In the US, emeralds
have been found in Connecticut, Montana, Nevada, North Carolina, and South Carolina. In 1997
emeralds were discovered in the Yukon. Synthetic emerald
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. 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 producing emerald crystals of 7 mm
of thickness. Gilson sold his production laboratory to a Japanese firm in the 1980s, but production
has since ceased; so has Chatham's, after the 1989 San Francisco earthquake.
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. Although not much is known about the original
process, it is assumed that Leichleitner emeralds were grown in acid conditions. Later, from
1965 to 1970, the Linde Division of Union Carbide produced completely synthetic emeralds
by hydrothermal synthesis. According to their patents, acidic conditions are essential to
prevent the chromium 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 in Russia, 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”.
Luminescence in ultraviolet light is considered a supplementary test when making a natural
vs. synthetic determination, as many, but not all, natural emeralds are inert to ultraviolet
light. Many synthetics are also UV inert. 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 has very strict regulations as to what can and what
cannot be called "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." Emerald in different cultures, and emerald
lore
Emerald is regarded as the traditional birthstone for May, as well as the traditional gemstone
for the astrological signs of Taurus, Gemini and sometimes Cancer.
One of the quainter anecdotes on emeralds was by the 16th-century historian Brantôme,
who referred to the many impressive emeralds the Spanish under Cortez had brought back
to Europe from Latin America. On one of Cortez's most notable emeralds he had the text engraved
Inter Natos Mulierum non sur-rexit mayor which referred to John the Baptist. Brantôme considered
engraving such a beautiful and simple product of nature sacrilegious and considered this
act the cause for Cortez's loss of an extremely precious pearl, and even for the death of
King Charles IX of France, who died soon after. India's most famous temple, the Madurai Minakshiamman
temple, has its chief deity as goddess Minakshi whose idol is made of emerald, most likely
carved out of a single emerald stone. Notable emeralds
Gallery
See also List of minerals
Mineral industry of Colombia References
Further reading Ali, Saleem H.. The Emerald City: Emerald
mining in Brazil http:www.uvm.edugemecology/brazil.html Cooper, J. C.. Brewer's Myth and Legend. New
York: Cassell Publishers Ltd. ISBN 0-304-34084-7. Hurlbut, Cornelius S.; Klein, Cornelis. Manual
of Mineralogy. New York: John Wiley and Sons. ISBN 0-471-80580-7.
Sinkankas, John. Emerald & Other Beryls. Prescott, Ariz.: Geoscience Press. ISBN 0-8019-7114-4.
Tavernier, Jean-Baptiste. Travels in India, Volume II. Edited by William Crooke and translated
by V. Ball. London: Oxford University Press. Weinstein, Michael. The World of Jewel Stones.
New York: Sheriden House. OCLC 519758. Wise, Richard W.. Secrets of the Gem Trade:
The Connoisseur's Guide to Precious Gemstones. Lenox, Mass.: Brunswick House Press. ISBN
9780972822398. OCLC 55662640. Online Emerald chapters.
External links ICA's Emerald Page International Colored Stone
Emerald Page