Characteristics of Colombian Emerald Specimens
Muzo, Coscuez and Chivor specimens exhibit many of the same elements in their respective matrixs'. 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 martix. 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.