The provenance of the finest emeralds
Emeralds are a green to bluish-green variety of the mineral beryl. Traces of the elements chromium and vanadium give these precious stones their distinctive colour and hue. However, emeralds can only be formed where the elements aluminium, silicon, beryllium and oxygen are also present in the same place. This unique and specific combination accounts for the rareness of theses stones. As recently stated by the GIA (Gemmological Institute of America): “Colombia has been the source of the finest emeralds for more than 500 years. The rich greens of Colombian emeralds are the standard by which all others are measured.”
Colombian emeralds are mostly produced in three main regions: Muzo; Chivor and Coscuez. For reasons of local geology, each of these regions produces stones with different characteristics, colours and hues. Muzo is associated with darker, pure green stones, whereas Chivor tends to produce lighter emeralds with a bluish-green tint and Coscuez is renowned for slightly yellowish-green gems. Due to the pre-eminence of Colombian emeralds, newer emerald finds in other locations have often been described in terms of their similarity to those of the main Colombian regions. It is interesting to note that it is the colour of the stone that attracts the title Muzo, Chivor or Coscuez, more than the specific geographical location of the stones origin within Colombia.
In geological terms, Colombian emeralds are the purest emeralds in the world due to the fact they are the only emeralds on the planet found in sedimentary rather than igneous rock formations. The proximity of the Andes mountains created the Colombian emerald deposits by virtue of tectonic activity. The saline solution, found only in igneous rock, ‘washed’ out any impurities such as iron that can reduce the clarity of an emerald. This process is also responsible for the highly desirable ‘deepness’ of colour found in Colombian stones. As is often the case with precious gems, a highly unique set of natural conditions can produce the most valuable stones. There are a number of small independent emerald mines in Colombia that lie outside of the main mining region but the stones from these tend to be inferior.
The legendary status of the Colombian emerald mines can be likened to that of the Argyle mine in Australia for diamonds, the Kashmir Sapphire mines or the Mogok mine in Myanmar for rubies. The region containing the Muzo, Chivor and Coscuez mines is known as Boyacá, the administrative department of which covers nearly 9,000 square miles of Colombia. The mines of Muzo consist of five underground sites, four of which are vertical mines which are over 100 metres deep and a one which is spiral bored and ventures down to more than 160 metres. The latter is large enough to utilise modern motorised machinery and it also enables geological research to take place alongside the mining operations. In the twenty-first century the Muzo mines can boast an excellent health and safety record and much has been done to improve the pay, conditions and welfare of the workers themselves.
Part of the modernisation of the emerald mining industry in Colombia is the heightened environmental consideration of such activities. The old methods of mining with highly dangerous dynamite and other high explosives has now been largely prohibited, both to protect the natural environment and also to prevent the quality of the rough emeralds from being compromised. In recent times a number of reforestation, hydroseeding and erosion control programmes have been introduced with the express aim of protecting this diverse rainforest ecosystem for future generations.
It has often been said that the Muzo emerald possesses the rare quality of an almost perfect hexagonal geometry. They are also renowned for their deep and intense hue and skilful cutting can carve the stone into a multitude of facets. As discussed in earlier articles all emeralds have fissures, due to their geochemical makeup, but the impact of these can be minimised by cutting the stone so that most of the fissures are positioned on the pavilion. This process sacrifices a small amount of weight in order to leave a face with greater clarity. Although many oils and resins are used by some, most experts only recommend the use of light cedar oil.
The development of workers’ rights in the Muzo mines has taken a major step forward in the past decade or so. For the first time the miners are now paid salaries (rather than on a highly manipulated commission structure) and they receive health care and other benefits, which are crucial in a country with a minimal national health service and welfare safety net. The employees of the mines are also undergoing on the job training and skilling, whilst their children are receiving full-time education in on site schools. All in all these measure represent significant progress compared with days gone by.
The technical difficulties of mining emeralds are brought into perspective when one considers the fact that the percentage of emerald crystal produced from the ore is a mere 0.0000006%, a figure some 10 times smaller than the comparable South African diamond mines. A further impediment to the rapid extraction of emeralds lies in the brittle nature of the stones, which do not respond well to the percussion and shockwaves associated with the use of explosives.