Birthstones: Emerald (May)

Who first beholds the light of day
In spring's sweet flowery month of May
And wears an emerald all her life
Shall be a loved and happy wife.

Emeralds should look somewhat familiar. Where have we seen this before?

Be₃Al₂(SiO₃)₆

A cookie for you if you knew right away that this is beryl, which has made an earlier appearance in this series as aquamarine.

Here is what the two look like if you compare them side by side.

Aquamarine

Emerald

The difference in color comes from a difference in the impurities in their crystal lattice. Aquamarine, as you may recall, owes its color to the play between different Fe ions (Fe2+ and Fe3+). Emerald, on the other hand, is green because of trace amounts of the metals chromium or vanadium (usually chromium).

The name "emerald" comes to English by way of Greek to Latin to French. The Greeks called it, simply, smaragdos, meaning "green" or "green gem," a name they may or may not have taken from the Sanskrit marakata. Over time, Latin added an excrescent "e" to form esmaraldus. That became esmeraude in French and, finally, emeraude  in English in the 14th century CE.

Emerald is another gemstone with a long and storied history. Records of it in Babylon go back as far as 4000 BCE. The earliest records of emerald mining in Egypt date to 2000 BCE, and possibly even earlier. Wherever they were initially discovered, trade carried emeralds all over the ancient world. Like many other gems, beliefs and powers ascribed to emeralds began to emerge:

• In Vedic astrology, emerald was (and still is) associated with the planet Mercury; carrying an emerald on your person was believed to strengthen one's Mercury-related abilities: intelligence, speaking, writing, communicating, traveling, and so on.
• For the Egyptians, emeralds were associated with fertility and rebirth and were highly prized by Cleopatra.
• Pliny the Elder said "nothing greens greener" than an emerald and held that gazing upon it improved eyesight. Romans believed that the gem ripened like a fruit, and that a pale stone, if left alone, would grow darker with age; they also believed that in the presence of falsehood an emerald would lose its color entirely, or even fall out of a setting.
• Aristotle recommended wearing emeralds for business transactions and court appearances, as it was thought to improve your presence and authority.
• In the Middle Ages, holding the gem in your mouth (don't swallow!) was believed to allow the individual to see the future and to discern falsehoods. It was also thought to help keep women chaste.

Emeralds were also part of the plunder the Spanish brought back from the New World—what the indigenous Muzo people thought of them is hard to tell, but at the very least they were a traditional part of religious and ceremonial garb.

Today, the best and richest sources of emeralds are still in Brazil and Colombia. Zambia is also another major producer. The output of the Egyptian mines, once the largest source of emeralds for the ancient world, continues today, but the stones it produces are no longer of any dazzling quality.

The Gachala Emerald, the largest emerald in the world. Found in Gachalá, Colombia. Currently residing in the Smithsonian Institute's mineral collection. Weight: 171.6 g, or about a third of a pound.

The chromium that creates the green in emeralds also leads to inclusions, imperfections, and fragility. This means that emeralds, while registering relatively high on the Mohs scale, are still quite brittle and delicate. As a result, they have been traditionally cut in an octagonal shape (as in the first picture: squares with the corners sliced off) to keep sharp, squared corners from chipping.This style is so associated with the stone that the such a shape is often referred to as an "emerald cut" regardless of the stone. That said, today you can find emeralds in any size or cut you want.

Most commercially available emeralds are treated to improve their clarity and stability. This is usually done with oil, which fills in any cracks and also binds the stone together; it also enhances color. Naturally occurring emeralds with dark, flaw-free coloring do exist, but they are extraordinarily rare and command a high price. They can also be synthetically grown. The US FTC requires that all synthetic or treated stones be marked as such, but something like 99% of emeralds on the market today are enhanced to some degree, so regardless of disclosure or markings, it's safe to assume any natural emeralds in your jewelry or collection has been oiled to a certain degree. Especially if you didn't pay an arm and a leg for them.