Short answer: emerald is the May birthstone. It is the green variety of the mineral beryl, colored by traces of chromium, vanadium and iron. Emerald rates 7.5 to 8 on the Mohs scale, but most stones contain many inclusions, so they are less tough than their hardness suggests. Colombia has produced the finest emeralds for more than 500 years. Almost all emeralds are treated with oil or resin to improve their clarity, which shapes how they should be cleaned.
What is the May birthstone?
May has one birthstone on the modern United States list: emerald. It ranks among the traditional "big four" precious gems, alongside diamond, ruby and sapphire.
What is emerald?
Emerald is a variety of beryl, a beryllium aluminum silicate, Be3Al2(SiO3)6. It is a close relative of aquamarine, the March birthstone, which is blue beryl. Pure beryl is colorless. In emerald, trace amounts of chromium, vanadium and iron produce the green, and the presence and relative amounts of each set the exact shade, from yellowish green to bluish green.
Only medium to dark green beryl is called emerald. Lighter-toned green stones are sold under the species name green beryl.
Why do emeralds have inclusions?
Most emeralds contain inclusions and tiny fissures. They are so common that the trade describes them as jardin, French for garden, after their mossy look. Because every stone's inclusions are different, they can even be used to identify a particular emerald. These inclusions are also why emerald's toughness is classed as poor, despite a hardness of 7.5 to 8.
Eye-clean emeralds of a vivid green, with only a little blue or yellow and a medium-dark tone, command the highest prices.
Where do emeralds come from?
Emeralds were mined in ancient Egypt from about 1500 BC, and those mines were worked by the Roman and Byzantine empires and later Islamic rulers. Mining there ended after the Colombian deposits were found.
- Colombia has been the source of the finest emeralds for more than 500 years, and Colombian stones are the standard others are measured by. Its three key areas are Muzo, known for darker pure green; Chivor, for lighter, slightly bluish green; and Coscuez, for slightly yellowish green. Colombia also produces rare trapiche emeralds, which show ray-like spokes of dark impurities.
- Zambia is the world's second biggest producer. Its emeralds tend to be bluish green and darker in tone.
- Brazil: the state of Minas Gerais has productive mines, including the Belmont mine and the Capoeirana area, worked largely by independent miners.
- Pakistan and Afghanistan are also important producers.
Emeralds and royalty
Emerald has enchanted royalty from the Egyptian pharaohs to the Inca emperors. Cleopatra was known for her passion for emerald. The Crown of the Andes, made in colonial South America, has a 24 carat emerald at its center and 442 more emeralds set in gold; according to lore, its largest stone, the Atahualpa emerald, was taken from the last Inca emperor by the conquistador Francisco Pizarro. Emerald and gold treasures were recovered from the wreck of the 17th-century Spanish galleon Nuestra Señora de Atocha.
What does the May birthstone mean?
The word emerald comes, through Latin, from the ancient Greek smaragdos, a green gem. The Roman author Pliny the Elder wrote that "nothing greens greener", and that gem cutters rested their eyes by looking at emerald. It was also thought to have magical powers: placed under the tongue, it was said to let a person see the future, and some believed it made its wearer an eloquent speaker and exposed lovers who made false promises.
These are traditions and beliefs, part of the stone's long history, not properties of the gem.
Are emeralds treated?
Almost all of them. Because inclusions are so common, emeralds are routinely filled to improve their apparent clarity.
- Oiling: cedar oil, which has a refractive index close to emerald's, is widely used to fill surface-reaching fractures. Synthetic oils and polymers are also used.
- Resins: the least expensive emeralds are often filled with epoxy resins.
- Dyeing: paler emeralds with many fractures may be dyed green.
Fillers vary in how stable they are, so a seller should tell you how an emerald has been treated.
Lab-grown emerald
Synthetic emeralds are grown by both hydrothermal and flux methods. They are real emerald in chemistry and structure, and they must be sold as synthetic or lab-grown.
How do you care for an emerald?
- Clean it gently with a soft brush and warm, soapy water. This is the safest method.
- Never use an ultrasonic cleaner. The vibration and heat can make fillers sweat out of fractures.
- Avoid heat and harsh chemicals, including hot dishwashing water, which can damage filled emeralds.
- Avoid sudden changes in air pressure, such as in an airplane cabin, which GIA lists among the risks.
- Store it apart from harder gems such as diamond, ruby and sapphire, which can scratch it.
May birthstone jewelry
Emerald rings, necklaces and earrings are classics, and faceted emeralds are most often given an oval cut or the signature "emerald cut", a rectangle with facets around the top edge. Many emeralds are also cut as cabochons. Because emerald is less tough than other popular gems, pendants and earrings face less risk of knocks than rings.
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Frequently asked questions
What is the May birthstone?
Emerald, the green variety of the mineral beryl.
What color is the May birthstone?
Green, from yellowish green to bluish green. Only medium to dark tones are called emerald; lighter stones are green beryl.
Why are emeralds so expensive?
Most emeralds contain many inclusions, so eye-clean stones of a vivid green are scarce, and those command the highest prices.
Are all emeralds treated?
Almost all emeralds are filled with oil or resin to improve their clarity. Some paler stones are dyed. Ask the seller how a stone has been treated.
Can I clean an emerald in an ultrasonic cleaner?
No. Vibration and heat can force fillers out of fractures. Use a soft brush and warm, soapy water instead.
Are emerald and aquamarine related?
Yes. Both are varieties of beryl. Emerald is green beryl colored by chromium and vanadium; aquamarine is blue beryl colored by iron.
Sources
- GIA, May Birthstone: https://www.gia.edu/birthstones/may-birthstones
- GIA, Emerald: https://www.gia.edu/emerald
- Wikipedia, Emerald: https://en.wikipedia.org/wiki/Emerald
- Wikipedia, Beryl: https://en.wikipedia.org/wiki/Beryl