The colour the trade calls Colombian.
Muzo is a mining district on the western flank of the Eastern Andes, in the Boyacá department of Colombia, one of the three classical Colombian sources alongside Chivor and Coscuez and the one whose name has carried the most weight in the trade for centuries.
Its emeralds formed where hot, beryllium-bearing fluids moved through Cretaceous black shale and reacted with the chromium and vanadium locked in the rock, crystallising in veins of calcite and pyrite. Because that host rock is low in iron, Muzo material tends toward a warm, slightly yellowish-green of exceptional saturation, the quality collectors mean by “Colombian green.” Colombian stones also tend to carry three-phase inclusions, a bubble of gas and a tiny crystal suspended in liquid, which laboratories read as a fingerprint of Colombian origin.
The finest and rarest of these show an effect the trade calls gota de aceite, “drop of oil”, a soft, roiled play of light within the stone, like honey stirred into water. It appears only in a handful of exceptional emeralds and is one of the hallmarks of the very top of the market.
The deposit has been worked since long before the Spanish arrived, first by the Muzo people, then formalised under colonial rule from the sixteenth century and through state and private hands since. It has been the reference point for fine emerald colour for five hundred years.
