Colombian Emerald Mining:
Will the Giant Awaken?
Colombian emeralds are mined from two belts within a mountain range known as the Eastern Cordillera. The western zone hosts, from north to south, the Peñas Blancas, Cosquez, La Pita, Muzo, and Yacopi mining regions; the eastern zone hosts the Chivor (Somondoco) and Gachala mines. These mines are located in the state of Boyacá, and access is difficult.
Colombian emeralds formed through a hydrothermal-sedimentary process. The geochemical processes for both the western and eastern zones are basically the same. The emeralds occur in organic rich shales and limestones. The fractures in the shales allowed hydrothermal fluids to infiltrate and deposit emerald and other accompanying minerals. This deposition occurred in several episodes involving heat and sometimes violent pulses of pressure. Fluid inclusions of the solutions from which the emeralds were formed became trapped during the crystallization process. These fluid inclusions represent a geological “fingerprint.”
Peñas Blancas emeralds are slightly bluish green, with little color zoning and a velvety appearance. One unique characteristic of the rough material is called “cascocho,” which refers to the crystals’ tendency to have pits and cavities due to secondary chemical etching. The abundance of quartz as a vein mineral differentiates Peñas Blancas from other emerald mines in the area.
Trapiche emeralds are perhaps the rarest and most memorable of “pattern” gems. Trapiche is the Spanish word for a spoked wheel used to grind sugar cane, which bears a striking resemblance to the pattern in these emeralds. Two distinct growth regimes are responsible for the formation. First, the central tapered core grows under hydrothermal conditions. Then, growth conditions change and both emerald and albite are formed. The hexagonal prism faces of the core maintain their uniform growth, producing pure emerald, while areas growing from the edges between prism faces do not and are filled with albite. This results in six sectors of clear emerald, and six of predominantly albite and minor emerald. Trapiche emeralds are cut into cabochons to display the beautiful spoke-like star. In the 1960s and 1970s, many large trapiches from Peñas Blancas found their way into collections all over the world.
Colombian emeralds are among the world’s finest in terms of quality. The Andean nation is still one of the main emerald producing countries, alongside Brazil and Zambia. A lack of investment and mechanization at aging mines led to a decline after easily accessible gems became scarce. Heavy overgrowth has inhibited geologic exploration, and prospecting has been hindered by remoteness, steep topography, and a difficult social climate. A sound government policy along with investment and thorough prospecting could tap the full potential of the Colombian emerald deposits.
Guy Lalous is a senior gemology instructor at the Academy for Mineralogy (ACAM) in Antwerp, Belgium and at Société Belge de Gemmologie (SBG) in Brussels. He is also an ACAM delegate at the Federation for European Education in Gemmology (FEEG) and a member of the Gemological Abstracts Review Board at G&G. He is an ACAM Graduate Gemmologist and holds a European Gemmologist degree.