Emerald (Be3Al2(SiO3)6) is a variety of the mineral beryl, colored green by trace amounts of chromium and sometimes iron. 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 on the 10 point Mohs scale of hardness. However, this Mohs rating can decrease, depending on the number and severity of inclusions in a particular stone.
Most emeralds are oiled as part of the post lapidary process. The amount of oil entering an emerald microfissure is roughly equivalent to the size of a period in print.
Emeralds come in many shades of green and bluish green. There is a wide spectrum of clarity, along with various numbers of inclusions. Most emeralds are highly included, so it is quite rare to find an emerald with only minor inclusions. Because of the usual inclusions, the toughness (resistance to breakage) is classified as generally poor.
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.
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 colorless beryl. The first commercially successful emerald synthesis process was that of Carroll C. 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 colorless 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, Chatham 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 colorless 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 colorant) 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.
Flux-grown synthetic emeralds fluoresce a dull red with long wave ultraviolet light, due to an indicator added during the process of synthesizing the emerald, whereas natural specimens do not.
Synthetic emeralds are often referred to as "created", as their chemical and gemological composition is exactly the same as its natural counterparts. The Federal Trade Commission (FTC) has very strict regulations as to what can and what cannot be called "synthetic" stone. The FTC says: "...[created stone must have] essentially the same optical, physical, and chemical properties as the stone named." Furthermore, all natural emeralds, with the exception of the red Bixbite beryls from Utah which are anhydrous, have water inclusions, as emerald is of hydrothermal origin. Flux synthetic emeralds have no water, an integral part of any natural beryl (this also accounts for flux-grown emeralds being more stable when subjected to high temperatures). Hydrothermally-grown emeralds, however, contain water molecules.
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.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, the Hebrew word "Nofech" in Exodus 28:18 means "Emerald", and was the stone on the Ephod representing the tribe of Judah. According to other commentaries, "Nofech" means "garnet", and another stone, the "Bareqet", representing the tribe of Levi, is thought to be emerald.
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.
Gachala Emerald (origin: Colombia)
Chalk Emerald (origin: Colombia)
Duke of Devonshire Emerald (origin: Colombia)