Emerald with host rock General Category Mineral Chemical formula Beryllium aluminium silicate with chromium, Be3Al2(SiO3)6::Cr Identification Color Green Crystal habit Hexagonal Crystals Crystal system Hexagonal Cleavage Poor Basal Cleavage (Seldom Visible) Fracture Conchoidal Mohs Scale hardness 7.5 - 8.0 Luster Vitreous Refractive index 1.576 - 1.582 Pleochroism Distinct, Blue-Green/Yellow-Green Streak White Specific gravity 2.70 - 2.78 Emerald (Be3Al2(SiO3)6) is a variety of the mineral beryl, colored green by trace amounts of chromium and sometimes vanadium. It is highly prized as a gemstone and by weight is the most valuable gemstone in the world, although it is often made less so by inclusions, which all emeralds have to some degree. Beryl has a hardness of 7.5 - 8 on the 10 point Mohs scale of hardness.[2] However, the effective hardness of an emerald is often reduced by fractures and inclusions. Most emeralds are highly included, so the toughness (resistance to breakage) is classified as generally poor.
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.
Most emeralds are oiled as part of the post lapidary process, in order to improve their clarity. Cedar oil is often used, having a similar refractive index, and it is a generally accepted practice. The U.S. Federal Trade Commission requires the disclosure of this type of treatment when a treated emerald is sold.[3] The amount of oil entering an emerald microfissure is roughly equivalent to the size of a period (full stop) in print[citation needed]. The use of green tinted oil is generally not considered acceptable by the gem trade.
Emeralds in antiquity were mined by the Egyptians and in Austria, as well as Swat in northern Pakistan.
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. It is named for the trapiche, a grinding wheel used to process sugarcane in the region. Colombian emeralds are generally the most prized due to their transparency and fire. Some of the most rare emeralds come from three main emerald mining areas in Colombia: Muzo, Coscuez, and Chivor. Fine emeralds are also found in other countries, such as Zambia, Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia.
The value of an emerald depends on cut, color, clarity, and carat. The characteristics of Colombian emeralds set the highest standards of quality.
Synthetic emerald
Emerald showing its hexagonal structureEmerald 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 colourless beryl. 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 is Pierre Gilson Sr., which has been on the market since 1964. Gilson's emeralds are usually grown on natural colourless beryl seeds which become coated on both sides. Growth occurs at the rate of 1 mm per month and a typical seven-month growth run produces emerald crystals of 7 mm of thickness (Nassau, K. Gems Made By Man, 1980).
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 Inbruck, 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 colourless beryl stones. Although not much is known about the original process, it is assumed that Leichleitner emeralds were grown on acid conditions. Later, from 1965 to 1970, the Linde Division of Union Carbide produced completely synthetic emeralds by hydrothermal synthesis. According to their patents (US3,567,642 and US3,567,643), acidic conditions are essential to prevent the chromium (which is used as the colourant) from precipitating. Also, it is important that the silicon containing nutrient be kept away from the other ingredients in order to prevent nucleation and confine growth to the seed crystals. Growth occurs by a diffusion-reaction process, assisted by convection. Typical growth conditions include pressures of 700-1400 bars at temperatures of 500 to 600°C with a temperature gradient of 10 to 25°C. Growth rates as fast as 1/3 mm per day can be attained
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 (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."
Wispy veil-like inclusions are common in flux-grown synthetic emeralds.
Cultural and historical/mythical usage
The Gachala Emerald is one of the largest gem emeralds in the world at 858 carats. 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 the Smithsonian Institution in Washington DC.Emerald is regarded as the traditional birthstone for May, as well as the traditional gemstone for the astrological signs of Taurus and Cancer.
According to Rebbenu Bachya, and the King James Version, the Hebrew word Nofech in Exodus 28:18 means Emerald, and was the stone on the Hoshen representing the tribe of Judah. However, the Septuagint translates the word as Anthrax, meaning coal, probably in reference to the colour of burning coal, and therefore many rabbinical sources, and most scholars, consider Nofech to mean a red garnet – traditionally called a carbuncle (gemstone), which happens to be the Vulgate's translation of the word. There is a wide range of views among traditional sources about which tribe the stone refers to.
Another candidate among the stones of the Hoshen for an Emerald is the stone referred to as a bareqet. Although bareqet means shiny, the Septuagint translates the word as Smaragdos, which is the Greek word that Emerald derives from. But Smaragdos is a false friend, as it actually just means green stone, and was used to refer to bright and translucent columnar green crystals – Heliodor, which is lighter than Emerald, is more likely to be the meaning. There is a wide range of views among traditional sources about which tribe this stone refers to as well.
The third candidate in the Hoshen for being an Emerald is the stone referred to as a Yasepheh. The New International Version translates the term as Emerald. The term actually means Jasper, and is cognate with the word; although Jasper is usually red, green Jasper was rarer and more valuable and the term Jasper was used in the classical era to refer to green Jasper. Jasper is very opaque, and quite dissimilar to Emeralds. For various reasons, some Targums translate the term Yasepheh as yellow zircon, red ruby, or Emeralds.
In some cultures, the emerald is the traditional gift for the 55th wedding anniversary. It is also used as a 20th and 35th wedding anniversary stone.
Famous emeralds Gachala Emerald (origin: Colombia) Chalk Emerald (origin: Colombia) Nidvin Emerald (origin: Colombia) Duke of Devonshire Emerald (origin: Colombia) Mackay Emerald Greenshorkire Emerald Edward the Confessor Emerald in the Imperial State Crown of Great Britain
