Characteristics of Emerald Specimens from Colombia
Ref: Delta Bravo
There are three main Emerald mining areas in Colombia: Muzo,Coscuez, and Chivor. These three areas are comprised of many individual"cortes" or mines. Muzo and Coscuez are on long term leases to two Colombian consortiums from the Colombian government and Chivor is privately owned. Muzo and Coscuez are much more prolific in production, thus the majority of the specimens we purchase are from these two areas. The best way to differentiate emerald specimens from these three origins is by carefully examining the individual characteristics of the crystals and the matrix.
The most obvious distinction between crystals from these areas is that the Coscuez crystals have a frequent occurrence of aggregate type formations with multiple terminations. These aggregates will very often have a stepped like look and sometimes take on a tabular appearance. A good example of this tabular type formation is a specimen from John Barlow's collection called El Silencio. It was named "El Silencio" because it came from a corte in Cosquez of the same name.
Another example of a multiple aggregate type formation is a specimen that was on a recent cover of the "The Mineralogical Record" (from Corte 35 in Coscuez). We called this specimen La Cresta because the crystal formation appeared similar to the crest on a roosters head.
Using color alone would make the identification process very difficult. The emerald crystals in Coscuez tend to exhibit a very wide range of colors and also tend to be more included. Emerald crystals from Muzo tend to have more saturated color than either Coscuez or Chivor. Chivor emeralds are best known for their bluish caste and generally have much less inclusions and lighter color than either Coscuez or Muzo. It must be stressed again that color alone in many instances will provide no clues in regards to origin.
In terms of size and shape, the emerald crystals from
Muzo tend to be shorter with a lesser likelihood of termination and
clustering. The crystals from Chivor frequently occur shaped like long
thin pencil leads.
Muzo, Coscuez and Chivor specimens exhibit many of the same elements in their respective matrix's'. The different combinations of these materials is what helps in distinguishing them from each other. Black and grey shale, white and grey calcite, and pyrite are the predominant elements that make up the typical Colombian emerald matrix.
In the Coscuez area, black shale in combination with either grey calcite or a rust colored layer of iron oxide or a gray calcite matrix by itself are the most common combinations found . Also thin veins of pyrite running through the black shale is quite common rather than crystallized nodules of pyrite. If you had to define any one thing as being the predominant characteristic in Coscuez matrix material it would have to be grey calcite. The photos of La Dosita and El Jardin are great examples of Coscuez emerald specimens.
In the Muzo area, three elements combined with the ubiquitous black shale provide the best clues in identifying a Muzo matrix. Those three elements are pure white calcite, crystallized pyrite and clear quartz. White calcite and crystallized pyrite are quite common with clear quartz being relatively rare. La Cruz from the collection of Joe and Ann Ondraka is a classic Muzo specimen. The white calcite and crystallized pyrite identify it immediately. The beautiful dark green color and bluish tint of the crystals are also typical of the El Indio corte (part of the Puerto Arturo area which produces the best quality emeralds in Muzo).
The Chivor mining area is the smallest area of three and is separate from Muzo and Coscuez which are adjacent to each other. The matrix material from Chivor tends to be much more fragile and "crumbly" in nature. Typically it is brown in color and is a brecciated mixture of calcite with layers of iron oxide. Iron stains are very common. Another type of matrix quite common in Chivor is a grey almost marble looking shale. Chivor like Muzo, frequently has crystallized nodules of pyrite occurring on the matrix. Because production in Chivor is sporadic and because the matrix material tends to crumble, fewer intact specimens are found. El Primero is an excellent example of a Chivor emerald specimen.
All three areas have many identical features in their matrix and crystal forms. But with careful inspection and examination of both the matrix and crystal properties, it can usually be readily determined from which area the particular Emerald specimen is from.
- Genesis Gems