Emeralds are formed when beryl, which is common in the Earth's continental crust and is made up of beryllium, aluminum, silicon and oxygen, has some of its aluminum atoms replaced with chromium or (rarely) vanadium, which exist in the oceanic crust and give emeralds their green color. Emerald crystals form a hexagonal prism with flat ends and have a mineral hardness of 7.5 to 8.
As the earth pushes its tectonic plates around, some of the continental plates get shoved under others and liquefy from the heat and pressure. If the upper plate is part of an oceanic plate, the liquified beryl may combine with the unfamiliar chromium or vanadium there and form emeralds. Because of this uncommon formation process, natural emeralds are even rarer than diamonds.
The word "emerald" derives from the Greek word for a green stone, smaragdos. Ancient emerald mines have been found in Egypt dating as far back as 2000 B.C., and they were worn by native Columbians when the Spanish conquistadors first arrived there.
Emerald was and is believed to give confidence, enhance creativity and mental capacities, instill marital loyalty and chastity, cure dysentry, prevent epilepsy, see the future, and drive away evil spirits. Its green color was also believed to rest and relieve the eyes. The ancient Romans associated emeralds with the reproductive forces of nature and dedicated gemstones to the goddess Venus. Early Christians used it as a symbol of Christ's resurrection, and the First Crusade returned to Europe with an emerald cup supposedly used by Jesus at the Last Supper.
The best emerald mines today are found in the mountains of Columbia, Brazil, Zambia, South Africa, western Australia, Pakistan, Russia, and Afghanistan.
Cleopatra had emerald mined near Aswan, Egypt in the first century B.C. In the 1930s, a German scientist finally perfected a process for producing synthetic emeralds, which appear very similar to natural ones but lack their identifying flaws. The unusual birthing process that creates natural emeralds almost always leaves small flaws, usually tiny flakes of the mica in which it's found. These are usually hidden by treating the gem with oil and are considered indicators of the gem's authenticity.
Emerald is the birthstone for the month of May and is the symbolic gemstone for the 20th and 35th wedding anniversaries.