Emerald is the most precious member of the Beryl family. It exhibits a distinct and recognizable pure green hue but can also be found in a bluish-green hue. On Mohs’ scale of hardness, emerald is 7.5-8. It has a vitreous luster and sources include Colombia, Zimbabwe, South Africa, Russia (Urals), Afghanistan, Australia (New South Wales, Western Australia), Ghana, India, Madagascar, Malawi, Mozambique, Namibia, Nigeria, Pakistan, Zambia, Tanzania, and the United States (North Carolina).
The beauty of Colombian emeralds, known for their extraordinary color and crystallization, is unique since their formation process occurred in a different geological environment than all the other known emerald deposits. They are found in black argillaceous limestone of the Upper Cretaceous age, which was deposited in a sea separating North and South America.
During the Continental drift, the Andes Mountains were formed, and beds that were originally at the bottom of the sea found themselves at the top of the mountains. While folding, the rocks fractured, which provided space for the growth of calcite veins. Hot magma followed by hot gases and fluids permeated through the cracks, bringing with them the elements necessary to crystallize emeralds. These gases were trapped in the crust of the fold in the eastern cordillera of the Andes by an impermeable shale formation. Since calcite veins are porous and permeable, the emeralds had an opportunity to crystallize while the gasses and fluids cooled off.
Color
Emerald exhibits an incomparable pure green hue but can also be found in a bluish-green hue.
Treatments and Enhancements
All emerald crystals go through the same six-part enhancement process to become the gemstones we are familiar with. These steps are sawing, performing, cutting, polishing, cleaning, and clarity enhancing. Virtually all emeralds require the process of clarity enhancement. This process involves immersing the emerald into a colorless medium. An infinitesimal amount of the clarity-enhancing medium penetrates the open fissures in the emerald. This volume is so small that it is usually not measurable by weight (as little as 1/100,000 of a gram).
It should be assumed that every emerald has been processed in this manner unless it has an accompanying laboratory report indicating that there is no evidence of a clarity-enhancement medium. Such extraordinarily rare stones command a considerable premium.
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