Emerald is gemstone variety of the mineral beryl, and has a unique shade of green, due to trace amounts of chromium and vanadium.
History and Origins
The word “emerald” is derived from the words “esmeraude” from Old French, “emeraude” from Middle English, “esmaralda” or “esmeraldus” from Vulgar Latin, and “smaragdus” from Latin, which originated from the Greek word “smaragdos.” All terms are variants of the same meaning, which is “green gem.”
Dating back to 1500 B.C. in ancient Egypt, this stone has been mined and sought after for centuries, often used in the decorations of sacred images.
The Romans believed that this gem detected falsehood and treachery in others by changing to a pale green color. Emeralds were considered very beneficial to the eyes, as it has recorded that the very short-sighted Emperor Nero used an emerald eyeglass to observe gladiatorial contests.
The Incas also owned many wonderful emerald stones, one of which has been described as being similar in size as an ostrich egg, believed to be inhabited by Esmeralda, the chief goddess of Peru.
Emerald’s more recent history commenced in South America in 1568, when Spanish conquistadors looted thousands of emeralds from natives and officially started mining emeralds themselves at the Muzo mine, which is still considered the world's largest deposit today.
Formation and Physical Properties
Emerald rough. Image credit to Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
Emerald’s formula is Be3Al2(SiO3)6, and has a formula mass of 537.50. Its crystal system is hexagonal, with a massive to well crystalline crystal habit.
The Gemological Institute of America categorizes emeralds as “type III,” meaning they are almost always included. As part of the beryl mineral family, emerald gemstones and their inclusions (or “jardin”) are a result of bits of liquids, gas, and other minerals like chromium and vanadium. These inclusions are a major source of the stone’s distinct green color.
Almost all emeralds sourced from Colombia are formed in hydrothermal veins when hydrothermal fluids escape from magma in the Earth’s crust. When these fluids offer acceptable concentrations necessary to form a natural emerald crystal, the stone may begin to take shape, as the fluids begin to cool in fractured deposit veins.
However, not all emerald crystals are developed this way. Some are formed in pegmatite deposits, which are similar to hydrothermal veins, but uses magma, or molten rock, as its primary agent, rather than hot water. During the magma’s cooling process, some elements are left in solution in the residual fluid.
Though emerald has a mineral hardness of 7.5 to 8 on the 10-point Mohs scale –which is generally quite high – almost 99% of these stones have inclusions, making their toughness (or resilience to breakage) fairly poor.
Colombia is by far the leading producer of emerald, comprising between 50 and 95% of the entire world’s production, depending on the source and grade yielded each year. The three most prominent mining areas in Colombia are Muzo, Coscuez and Chivor.
Other major localities that produce emerald gemstones include:
United States of America – in Connecticut, Montana, Nevada, North Carolina and South Carolina
Zambia – the world’s second largest producer of emerald; much of which is found in Kafubu River deposits