Chivor Mine, Chivor, Boyacá Department, Colombia
Chivor is the leading commercial deposit in the eastern emerald-bearing region. It was mined by local indigenous people, and was rediscovered by the Spaniards, who exploited and later abandoned it. Modern exploitation began with rediscovery in 1896. Emerald mineralization is geologically controlled by the San Fernando fault at its intersection with a north-northeasterly striking tectonic zone of jointing.The emerald-bearing veins and veinlets form a series of transecting and concordant bodies in bluish gray schists, which are up to 15 cm thick and 65 m long. The emerald is initially associated with albite (clevelandite) and fresh or oxidized pyrite.
Emeralds from the veins and "pockets" in the shales are represented by prismatic often short-columnar crystals to 3 cm long. Larger emeralds, some as much as 15 cm in length, are occasionally recovered. Some are of very high gem quality and have established worldwide recognition for the Colombian emeralds (example is Patricia emerald - 682 carats).
The emerald colour varies from light green to bright and deep green, it depends on the content of chromophore admixtures. Chivor emeralds have a bluish tint. Solid inclusions are pyrite particles.
Ref: E.Ya. Kievlenko (2003) Geology of gems, pp. 100 - 101