Selasa, 18 Disember 2012


Emeralds Around the World
Natural Colombian Emerald
Colombian Emerald

Colombia is most the most famous source for emeralds, but emeralds have been mined in many locations in the world. In fact recent decades have seen production increase from new deposits in south America and Africa.
The most famous deposit in Colombia is the Muzo mine northwest of Bogota. This deposit was first mined by Native Americans but was eventually abandoned and then rediscovered in the 17th century. The Muzo mine yields fine quality emerald of a deep green color. Another important deposit is the Chivor Mine, northeast of Bogota. More recently new deposits have been discovered which look promising for the future. Still, only a third of the emeralds mined in Colombia are worth cutting.
Brazil has emerald deposits in Bahia, Goias and Minas Gerais. The color of the Brazilian stones is lighter than the Colombian material; they tend to a yellow-green. But the Brazilian emerald is often relatively free of inclusions. New deposits have been found since 1980 and Brazil is now one of the most important suppliers of emeralds in the world.
Natural Brazilian Emerald
Brazilian Emerald
In the last several decades, increasing quantities of emeralds have been found in a series of small deposits in East Africa, particularly in Zimbabwe, Zambia and Tanzania. The East African emeralds are quite strong in color, sometimes with the desirable blue-green hue. The most famous of these emeralds are the ones from Sandawana in the south of Zimbabwe. The Sandawana crystals tend to be small but are very high quality.
Emeralds also are mined in South Africa, in the northern Trasvaal. Modern mechanized mining is carried out at the Cobra and Somerset mines, but only about 5% of the product is of good quality. Most stones are light in color or heavily included and only suitable for cabochons.
Other noteworthy emerald deposits are in India and Pakistan as well as in the Ural Mountains in Russia. Less important deposits have been found in Afghanistan, Australia, Ghana, Madagascar, Malawi, Mozambique, Namibia and the United States (North Carolina). In Europe, emeralds have been found in Austria and Norway.
The most famous emerald mines of antiquity were in Egypt. Known as the Cleopatra Mines or Mons Smaragdus (Emerald Mountains),they were worked as early as 2000 B.C. The mines were also worked during later centuries but they were abandoned after the Spaniards discovered emeralds in Colombia in 1545.

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 breakage) is classified as generally poor.

Etymology

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").

[edit]Properties determining value

Cut emeralds
Emeralds, like all colored gemstones, are graded using four basic parameters – the four Cs of Connoisseurship: ColorCutClarity andCrystal. 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"[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 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.[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]

[edit]Color

Scientifically speaking, color is divided into three components: huesaturation 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.[6] 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.[7]
Emeralds are green by definition (the name is derived from the Greek word 'smaragdus', meaning green).[8] 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.[9]

[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.[4] 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.[10] 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; noneminormoderate 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.[4]

[edit]Emerald localities

Spanish emerald and gold pendant exhibited at Victoria and Albert Museum.
Emeralds in antiquity[when?] were mined by the Egyptians and in India and Austria.[11]
A rare type of emerald known as a trapiche emerald is occasionally found in the mines of Colombia. A trapiche emerald exhibits a "star" pattern; it has raylike spokes of dark carbon impurities that give the emerald a six-pointed radial pattern.[citation needed]Emeralds come from three main emerald mining areas in Colombia: Muzo, Coscuez, and Chivor.[12]
Colombia is by far the worlds largest producer of emeralds, constituting 50-95% of the world production, with the number depending on the year, source and emeralds grade.[13][14][15][16] Emerald production in Colombia has increased drastically in the last decade, increasing by 78% in 2010 compared to production in 2000.[17]
The emerald deposits of Zambia in the Kafubu River (Kagem Mines),about 45 km southwest of Kitwe, produced around 20% of world production of gem quality emeralds in 2004, making the Kafubu area mines the second in world wide production after Colombia.[18] In the first 6 months of 2011 Kagem mines produced 3.74 tons of emeralds.[19] Zambian emeralds have very high quality, they are less porous and less brittle than Colombian emeralds, with more even color.
Emeralds are also found in other countries, such as AfghanistanAustralia, Austria, Brazil,[20] BulgariaCambodiaCanada,ChinaEgyptEthiopiaFranceGermanyIndiaItalyKazakhstanMadagascarMozambiqueNamibiaNigeriaNorway,PakistanRussiaSomaliaSouth AfricaSpainSwitzerlandTanzaniaUnited StatesZambia and Zimbabwe.[1] In the US, emeralds have been found in ConnecticutMontanaNevadaNorth Carolina and South Carolina.[1] In 1998 emeralds were discovered in the Yukon.[citation needed]

[edit]Synthetic emerald

Emerald showing its hexagonal structure
Emerald is a rare and valuable gemstone and, as such, it has provided the incentive for developing synthetic emeralds. Both hydrothermal and flux-growth synthetics have been produced, and a method has been developed for producing an emerald overgrowth on colorlessberyl. The first commercially successful emerald synthesis process was that of Carroll Chatham. Because Chatham's emeralds do not have any water and contain traces of vanadate, molybdenum and vanadium, a lithium vanadate flux process is probably involved. The other large producer of flux emeralds was Pierre Gilson Sr., which has been on the market since 1964. Gilson's emeralds are usually grown on natural colorless beryl seeds which become 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.[21] Gilson sold his production laboratory to a Japanese firm in the 1980s, but production has ceased since; so did 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 InnsbruckAustria, 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.[citation needed] Later, from 1965 to 1970, the Linde Division of Union Carbide produced completely synthetic emeralds by hydrothermal synthesis. According to their patents,[22][23] 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 in Russia. They have succeeded in synthesizing emeralds that have similar chemical composition as emeralds in alkaline deposits in Colombia, hence they are called “Colombian Created Emeralds” or “Tairus Created Emeralds”.[24] 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.[25]
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 "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."[26]

[edit]Emerald in different cultures, and emerald lore

The Gachala Emerald is one of the largest gem emeralds in the world, at 858 carats (172 g). This stone was found in 1967 at La Vega de San Juan mine in Gachalá, Colombia. It is housed at the National Museum of Natural History of theSmithsonian Institution in Washington, D.C.
Emerald is regarded as the traditional birthstone for May, as well as the traditional gemstone for the astrological signs of TaurusCancer and sometimes Gemini. 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 engravedInter Natos Mulierum non sur-rexit mayor ("Among those born of woman there hath not arisen a greater,"Matthew 11:11) 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 (to which he dedicated a work, A beautiful and incomparable pearl), and even for the death of King Charles IX of France, who died soon after.[27] "The Attenbury Emeralds" is a detective story in which Lord Peter Wimsey must solve several emerald-related mysteries.

Emerald crystal from Muzo, Colombia

Emerald crystal from Muzo, Colombia
General
CategoryBeryl variety
Formula
(repeating unit)
Be3Al2(SiO3)6
Crystal symmetry(6/m 2/m 2/m) – Dihexagonal Dipyramidal
Unit cella = 9.21 Å, c = 9.19 Å; Z = 2
Identification
Formula mass537.50
ColorGreen shades to colorless
Crystal habitMassive to well Crystalline
Crystal systemHexagonal (6/m 2/m 2/m)Space group: P6/mсc
CleavageImperfect on the [0001]
FractureConchoidal
Mohs scalehardness7.5–8
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
UltravioletfluorescenceNone (some fracture filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not)

Gallery


EMERALD ROUGH 



THESE STONES WERE MINED IN BRAZIL  FROM A LARGE PARCEL DIRECT FROM THE MINER. THEY ARE OF A SMALL SIZE BEST SUITED TO BEADS -GEMS STONE PAINTINGS ECT. THEY ARE NATURAL STONES UNTREATED BUT STORED IN OIL.
SIZE OF LARGEST STONE  6 X 5 X 4 MM APPROX.
 WEIGHT OF PARCEL  102.80 CTS APPROX.

EMERALD IS A VARIETY OF THE MINERAL BERYL, COLORED GREEN BY TRACE AMOUNTS OF CHROMIUM AND SOMETIMES VANADIUM. BERYL HAS A HARDNEDD OF 7.5 – 8 ON THE 10 POINT MOHS SCALE OF HARDNESS. MOST EMERALDS ARE HIGH INCLUDED, SO THE BRIGHTNESS (RESISTANCE TO BREAKAGE) IS CLASSIFIED AS GENRALLY POOR. THE ORIGIN OF THE WORD “EMERALD” IS SAID TO BE A SANSKRIT WORK MEANING “GREEN”. EMERALDS COME IN MANY SHADES OF GREEN AND BLUISH GREEN. THERE IS A WIDE SPECTRUM OF CLARITY, DEPENDENT ON THE INCLUSIONS AND FRACTURES IN THE CRYSTAL. CLEAR STONES WITH DARK YET VIBRANT COLOR COMMAND THE HIGHEST PRICES. THE VALUE OF AN EMERALD DEPENDS ON THE CUT, COLOR, CLARITY AND CARAT WEIGHT.





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. ] The amount of oil entering an emerald microfissure is roughly equivalent to the size of a period (full stop) in print. The use of green-tinted oil is generally not considered acceptable by the gem trade






click for full size

(MGW) EMERALD ROUGH 0.85 CTS FP 1141
mineralgemworld

KASHMIRE EMERALD ROUGH 6.50 CTS [MX 6835 ]
mineralgemworld

KASHMIRE EMERALD ROUGH-NEW MINE 2.20 [1622]
QUALITY ROUGH


COLOMBIA EMERALD ROUGH 2.00 CTS [F1632 ]
QUALITY ROUGH






About Emerald Rough

Natural Emerald rough is ideal for beginners or professional cutters. Rough is ready to shape and polish or facet or make beads on lapidary equipment.
Emerald is a variety of the mineral beryl, coloured green by trace amounts of chromium and sometimes vanadium. Columbia has been the most important source of finest grade emeralds. It is a highly sought-after precious Gem, the most famous and favoured green stone, which for centuries has been widely used in the creation and encrustation of jewellery and everyday items. In combination of its colour, together with the durability and rarity makes it one of the most valuable gemstones. Emerald is the birthstone for May.
Emeralds have one of the longest histories of all gemstones, since the time of Cleopatra and ancient Egyptian pharaohs. Dating back 1500 BC where ancient mining tools have been discovered at the entrance of emerald mines. Emeralds have set the standard for the ultimate colour in green gemstones. -
Their Chemical Composition number is Si03 and its hardness ratio is between 6 to 8. When purchasing an emerald, colour is the most important factor. An optimum choice would be a consistent rich, luminescent velvety green colour throughout the stone. As emeralds gemstones are both rare and valuable, it gives opportunity for development of synthetics. There are many fakes and synthetics, therefore any important purchase of emerald is recommended to have a Gemological certificate for authenticity, retrieved from a reputable Gemological laboratory. 
Emeralds are very fascinating gemstones. Emeralds are admired for their radiant green color. As with natural Emerald stones, slight inclusions are tolerated.  Top quality Emeralds, compared to diamonds are even more valuable than the diamonds.
The Incas and the Aztecs of South America regard the Emerald crystals as a Holy gemstone.
 In Ancient times Emeralds are highly regarded for their healing properties and also Promises “good luck”, therefore the Indian Maharajahs treasure chest contain an assortment of Emerald stones.
The green color of the Emerald represents harmony, and love of nature. Green is perceived as colour that never tires the eyes.
The Zimbabwe emeralds are the oldest gemstones in the world. Emeralds were already growing 2600 million years ago. Pakistan emeralds were found 9 million years ago. Where do they come from and how is it that they exist at all? In order to answer these questions, we need to look far, far back into the time of the emerald's origin. Emeralds from Zimbabwe are among the oldest gemstones anywhere in the world. already growing 2600 million years ago.
Emerald rough suppliers on GemRockAuctions include Quality Rough, Stars and Gems,Mineralworld,Treasures of The World as manufactures of Emerald rough for cabbing or carving into emerald beads.,Emerald rocks minerals rough from gemstone wholesalers on GemRockAuctions.
For any investors, collectors or lovers of this gem, it is recommended to have a Gemological identification certificate for authenticity. It is an independent report from an approved gemmology laboratory, issued by an independent gemologist