May's Birthstone - Emerald
inMay 7, 2008 - 6:57am
The primary May birthstone is Emerald, and the unique green color makes it a perfect stone for a mid-spring celebration.
While Emeralds have many sources, ancient and modern, it was the exploration of South America in the 16th century that made Emerald widely available. Many of the world’s finest Emeralds come from South America.
It is a variety of the mineral Beryl, as is Aquamarine. While many Aquamarines are very “clean” to the eye, with virtually no visible inclusions, this cannot be said of Emerald. Sellers of emerald even use the term “jardin”, French for “garden” to describe the interesting internal characteristics of the stone. The actual name Emerald probably comes from a Sanskrit word meaning “green”.
Small traces of chromium are responsible for the green color. Some Emeralds are colored by vanadium, and some gemologists believe these stones should not be sold as Emeralds. Vanadium colored stones often exhibit fewer inclusions than chromium colored stones. There is also a pale green beryl, colored by iron, which resembles greenish Aquamarine more than it does Emerald. This material should be represented and sold as Green Beryl, although not all stone vendors agree.
Due to the presence of natural inclusions, which often break the surface of stones, virtually all natural Emeralds are treated to improve their appearance. Cedar wood oil has been used for centuries to mask these inclusions. Colored oils which mask the appearance of inclusions and improve the color are also used, though frowned on by many. Modern optical mediums, such as Opticon have also been used, and some stones are fracture-filled. In this process, a glass like material actually fills the fissures and voids in the stone.
All these treatments require disclosure, and it is best to assume that an Emerald has at least been oiled to improve its appearance. It has been reported that some stones are being irradiated to improve their appearance.
While relatively hard, with a Moh’s scale rating of 7.5-8, Emerald is considered rather brittle, and the presence of inclusions makes this stone rather prone to chipping and fractures. Antique pieces with Emerald will often show wear to the stones, with a loss of crisp facet edges, and some replacement stones may often be seen in older cluster designs.
Certain color ranges of Emerald are so closely associated with Columbian sources that Columbian Emerald is often used as a color description, and may not always refer to the actual country of origin. The Muzo mine in Columbia is legendary for the fine stones produced, which include the Devonshire Emerald. This uncut stone, weighing over 1300 carats, was given to the Duke of Devonshire by the Emperor of Brazil in 1831. Muzo is located in a large area known for Emeralds, northeast of Bogota, Columbia. The Chivor mine, also in Columbia, produced the stone that was fashioned into the Patricia, a 632 carat gem named after St. Patrick.
Emeralds are also produced in other parts of South America, Brazil produces some, along with much material which is more properly identified as Green Beryl. Zambia, Zimbabwe, Afghanistan, Pakistan, Russia, some former Soviet republics, and Australia are also commercial producers of Emerald. Jamie Hill of Hiddenite, North Carolina gained a great deal of notoriety 10 years ago when he discovered a great source of Emeralds on his property. This find, located at a shallow depth, has produced some phenomenal stones, including rough stones with weights in excess of 800 carats. Some gems fashioned from this rough have sold for over $1,000,000.
Chrome Tourmaline and some green Garnets can be mistaken for Emerald. Chrome Tourmaline is seldom encountered in older pieces. Of the green Garnets, Tsavorite is a newer arrival on the gem scene. Both Tsavorite and green Demantoid Garnet have an optical appearance which is slightly different than Emerald, but the color range may mimic that of Emerald.
Emerald may also be imitated by glass, doublets, and by synthetic Emerald. Synthetic Emeralds can be made by several different processes, and those made by Chatham and Gilson are probably the best known. Carroll Chatham developed his process in 1938, so these stones have been available for decades and can be present in vintage pieces. Doublets, often formed of garnet and glass components, have also been in use for quite a while, and were often used in moderately priced birthstone jewelry and Mother’s rings. Under magnification, the joint line is often visible on the crown of the stone near the girdle. Ultra-violet lighting will often reveal this.
Natural and simulated Emeralds may both be seen as faceted stones, cabochon stones, and beads. Variations in quality and treatment can create a vast range of prices for Emeralds. They are heat sensitive and often need removed from settings for repair work. Emeralds should never be cleaned with steam cleaners or ultrasonics.