Emerald
From Free net encyclopedia
- For other uses, see Emerald (disambiguation).
| Emerald | |
|---|---|
Image:Emerald rough 300x422.jpg Emerald with inclusions | |
| 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 iron. It is highly prized as a gemstone and by weight is the most valuable gemstone in the world, often made less so by inclusions, which all emeralds have. Beryl has a hardness of 7.5 on the 10 point Mohs scale of hardness. However, this Mohs rating is often adversly affected and can decrease, depending on the number and severity of inclusions in a particular stone.
Synthetic emerald
Emerald is a rare and valuable gemstone and, as such, 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. Flux-grown Synthetic emeralds fluoresce a dull red with long wave UV 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 same as its natural counterparts. The FTC (Federal Trade Commission) has very strict regulations as to what can and what can not be called “synthetic” stone. The FTC says: (created stone must have) “...essentially the same optical, physical, and chemical properties as the stone named.”[1] Furthermore, all natural emeralds 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). Hydrothermaly-grown emeralds, however, contain water molecules. Joint Venture Tairus is the largest producer of synthetic emeralds today.[2] Wispy inclusions are common in flux-grown synthetic emeralds.
Culture and historical/mythical usage
Emerald is regarded as the traditional birthstone for May. According to legend, the emerald has the power to protect the chastity of the wearer and to ward off evil spirits. Furthermore, it was used as a cure for epilepsy and dysentery as well as to aid weak eyesight.
According to Rebbenu Bachya, the word "Nofech" in the verse Exodus 28:18 means "Emerald" and was the stone on the Ephod representing the tribe of Judah. According to other commentaries, "Nofech" meant "garnet". Another stone, "Bareqet", representing the tribe of Levi, is instead thought to be the emerald.
In some cultures the emerald is the traditional gift for the 55th wedding anniversary. It is also used as the 20 and 35th wedding anniversary stone.
References
- Cooper, J.C. (Ed.) (1992). Brewer's Myth and Legend. New York: Cassell Publishers Ltd. ISBN 0-304-34084-7.
- Sinkankas, John (1994). Emerald & Other Beryls. Geoscience Press. ISBN 0801971144
- Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York: John Wiley and Sons. ISBN 0471805807
- Weinstein, Michael (1958). The World of Jewel Stones. Sheriden House.ar:زمرد
bg:Изумруд da:Smaragd de:Smaragd et:Smaragd es:Esmeralda fr:Émeraude he:ברקת id:Zamrud ja:エメラルド lt:Smaragdas nl:Smaragd no:Smaragd pl:Szmaragd pt:Esmeralda ru:Изумруд sv:Smaragd tr:Zümrüt vi:Ngọc lục bảo zh:祖母綠