Geologically speaking
Most of Colombia’s emerald deposits are on the eastern ridge of the Andes Mountains, which run northeast-southwest through the country. The three main mining areas are Chivor, in the eastern part of Boyacá Department, and Muzo and Cosquez in the western section. Colombian emeralds are unique, as they are associated with sedimentary rock rather than igneous rock. The tectonic movements that created the Andes forced the elements beryllium, chromium, and vanadium—which give the gem its green colour—into liquid and gaseous states that moved into cracks in the sedimentary material. They eventually cooled and crystallized in veins with hydrothermal brine that washed out the iron and other impurities. Often associated with quartz, pyrite, calcite, albite, and other minerals, the deposits of this vein-type ore are estimated to have been formed 40 million to 65 million years ago. The heavily faulted and folded sedimentary layers are mostly black shale and argillite.
