Searching for Green in Black and White
Emeralds from the Muzo, Coscuez and Chivor mines in Colombia
Colombian emeralds are widely considered to be the best emeralds on the planet. The highest quality emeralds of Colombia are extremely rare and fetch massive sums of money. In this report I will be focussing on the emeralds from the Muzo, Coscuez and Chivor mines which are part of the ‘Western and Eastern emerald belts’ in the Boyacá region of Colombia. I will begin with a brief summary of the history of this region, which is relevant considering how unstable it is in modern times. This report will enable the reader to understand the subtle geological differences between each of these mines, and also learn why the emeralds that are extracted from them are so prized. I'll explain why mining and even buying or selling Colombian emeralds is not an easy task. Up until the past decade, Colombia was the leading producer in emeralds and this is due to reasons which I will cover.
The indigenous peoples (Known as Incas or Indians) of South America have been mining and worshipping emeralds for thousands of years. Things changed when the Spanish explorers first discovered the emeralds in the 16th century while on their conquest of South America. The Spanish, led by Gonzalo Jimenez de Quesada, were eager to know where these amazing green stones were found and happened to find a local tribe of Indians east of modern day Bogota in 1537. This location is near the modern day Chivor mine and the tribe in this area was easily conquered. This tribe mentioned more emerald mines to the northwest in the Muzo district. However, the Muzo tribe was extremely fierce and would not give up without a fight. In 1538, Spanish soldiers lead by a Captain Luis Lanchero set foot in this new area clad in steel swords, armour and firearms, only to be welcomed with a bloody fight and forced to retreat.
The Muzo tribe surprised the Spanish soldiers with poison arrows, jungle traps, camouflaged pits and numerous fortifications. One can only imagine how difficult and tedious the battles would have been for the Spanish. It took until 1558 for the Spanish Captain Lanchero to finally defeat the Muzos only by introducing a new weapon: ferocious European hunting dogs, which "caused havoc and confusion in the ranks of the Indians" Ron Ringsrud (1986). Shortly after the battles, the Muzo and Coscuez mines were under Spanish control.
Unfortunately for the defeated Indian tribe, they were forced into slave labour and thousands died because of this, as well as from poverty and diseases introduced by the Spanish. Over the centuries these mines would be abandoned and re-opened because of low emerald production due to ownership issues, mining accidents and lack of labour. In 1871 the Colombian government officially claimed ownership of the mines in the Muzo district, including Coscuez, and have been systematically leasing them in 5 year terms to mining companies. In 1982, this process was discontinued due to ineffective mining methods such as explosives and bulldozing. Because of this, 10 year leases were granted for mining companies such as: Tecminas and Coesminas who developed tunnelling methods because the alternative was too destructive. The Chivor mine is currently a privately owned mine.
There are several major emerald mines littered around the Boyacá region of Colombia, the majority being to the northwest near the Muzo district. These mines are mined exclusively for emeralds. This region of the country has intimidating terrain and consists of hot climates, dense jungle, rivers and large mountainous valleys, which makes exploration very difficult. The Chivor mine (part of the Chivor district) is situated roughly 75km slight northeast of Bogota (Colombia's most populous and capital city) and the mine itself is at an elevation of about 2300m above sea level (figure 3).
The Muzo mine (part of the Muzo district), which is the largest mine in Boyacá, is located roughly 95km northwest of Bogota and is also the name of a small town which is 8km west of the Muzo mine (figure 4). Unless you can get there by helicopter, it can take a few hours to commute there by four-wheel drive because of the rough terrain and poor windy roads. There are even points where you can drive straight off a cliff if you are not careful. Not only is the terrain rough, but there is a risk of being kidnapped, robbed, or even killed by local gangs or criminals, so it is essential to have a guide with you if you are a foreigner. The mine itself is at an elevation of about 800m above sea level (figure 5). The Coscuez mine is just 10km north of the Muzo mine and is roughly 1120m above sea level.
The geological surroundings of the Colombian emerald mines mostly consist of sedimentary rocks such as shale and limestone, including some minor igneous and metamorphic rocks as well as other minerals I will mention later. Basically, within these sedimentary rocks are veins of minerals such as calcite, which can also carry emerald crystals, and these minerals have grown in hydrothermal deposits. "The emerald, in its mode of occurrence, is unique, for it is found exclusively in its primary situation, that is to say, in the rock in which it was formed" Dr. Max Bauer (1904).
The goal is simple for the miners: find the white to get the green. At Muzo, the ‘white’ represents veins of calcite in which the ‘green’ emerald crystals are found in (figure 6). They are buried within "highly folded, faulted and fractured carbonaceous shales and thinly bedded limestones" Peter C. Keller (1981). In the Muzo district (Both Coscuez and Muzo mines) the emeralds which are found in these mines are from what is called the Villeta formation of the lower cretaceous age which dates back 120-130 million years, "The Villeta formation consists of a great thickness of black, carbonaceous shales and minor amounts of limestone" Ron Ringsrud (1986).
During these years, hydrothermal fluids filled into fractures caused by fault zones (or weak spots) in these sediments of rock, depositing minerals such as: calcite, dolomite, emerald, pyrite, quartz, albite, fluorite, parisite and baryte. Immense heat and pressure caused by the movement in these fault zones is responsible for the deposition of these minerals and these tectonic shifts would occur over millions of years and are happening still. The white calcite veins are what the miners are always searching for and these are usually 35cm thick and several meters in length, but can of course exceed this depending on the deposit.
The rock sediments at Chivor consist of heavily faulted and folded shales and argillites with some limestone. The sediments are also of lower cretaceous age. At Chivor however, the emeralds don't occur with calcite but instead occur in veins of pyrite (figure 7), albite, or pyrite with albite, ‘It is stressed that there have been no reports of emeralds occurring in calcite or dolomite at Chivor, both quartz and pyrite are very common there’ Peter C. Keller (1981). Emerald crystals are generally small and can occur in groups or just be a single crystal; in rare cases they exceed the size of a man's thumb. The largest known single crystal found in Colombia, called the Emilia, is 7025 carats (1.4kg) which was discovered in 1969 but as of now its location is unknown.
The mining of emeralds from Muzo, Coscuez and Chivor is relatively similar. The emeralds have been mined through a combination of techniques over the years such as: open-cut mining, tunnelling, use of heavy machinery such as bulldozers, jackhammers, drills, explosives such as dynamite and simply an individual using basic tools such as shovels, crowbars and pickaxes.
The issue with the leasing of the mine is that the lessee typically will employ the fastest and most destructive method to extract as many emeralds as possible, with no regards to environment or conservation. Over centuries there have been problems with thievery and managers pocketing emeralds for themselves, but I will focus on the methods used rather than this.
I'll use an example from the Muzo mine. Initially, open-cut mining was the main method used to extract emeralds up until 1982 when they began tunnelling because there was very little calcite and emeralds to be found on or near the surface. Open-cut mining can consist of workers digging on benches all over the sides of the mountain using pickaxes, crowbars or shovels. They dig through the black shale looking for calcite veins which will lead to the emeralds.
This process also involves removing tonnes of shale off the mountain itself by flushing it away with water supplied from reservoirs above the workings, in which this ‘garbage rock’ is hauled down the side of the mountain into the nearby Rio Itoco river. This is where thousands of ‘guaqueros’ (translated to treasure hunters) would be digging through these rocks in the hopes of finding emeralds missed by the workers further up the mountain (figure 10). This kept the locals happy and they could manage to live off this. It is important to note that in the past few decades the number of guaqueros has drastically reduced because almost all the mining at Muzo is now done in tunnels. Between the 1960s-1980s lease holders would start using bulldozers and dynamite because they wanted to extract as many emeralds as possible in the 5 years.
An example of the open-cut method: There would be about 20-30 workers who would plant dynamite around an area they wish to explore for calcite veins. After blasting the area, they would roll over and remove the fragmented rocks with the bulldozers creating gullies and removing the black shale to find the white emerald bearing calcite (figure 9). In which the group of workers would begin to dig through the veins with pick axes, crowbars or shovels, while finding and pulling out the best pieces they could find and sorting through it, in which the manager would keep the best rough emerald crystals found and reward the workers with lesser quality rough emerald crystals. The ‘junk rock’ would get heaved off the side of the mountain where the guaqueros would scavenge it and hopefully find decent emeralds. This blasting and bulldozing process would cause massive destruction and they would even destroy potentially expensive and rare specimens of emerald.
Tunnelling involves digging through the side of the mountain, either horizontally, at an incline or decline and following the emerald bearing calcite veins until they stop (figure 11). At this point they will search for another calcite vein to follow. These tunnels can stretch over a thousand metres into the mountain. This is a dangerous method and the tunnels can get very humid, which is why they have pipes and wires which supply ventilation, power and water to wash away the shale in the tunnels. The shale is removed by hand, or rolled out in carts on tracks through the shafts and dumped down the side of the mountain. One of the reasons that emerald exploitation has had issues and has declined is because of the lack of infrastructure, particularly in the Muzo district. The London based company ‘Gemfields’ is planning on purchasing one of the mines in the near future, so it will be interesting to keep up to date with that and see how well they can improve the infrastructure of the mine they work on.
So what is all the fuss about? Emerald. This rare mineral is part of the beryl species of crystals. It crystallizes in the hexagonal crystal system and generally its crystal habit is that of long 6-sided prisms with smooth faces and flat terminated ends, known as the basal plane (at a right angle to the crystal length). Colombian emerald crystals typically terminate with these basal planes, however they can also grow in different forms such as having bipyramid terminations at the end of the crystals.
It is a silicate material with the presence of aluminium and beryllium, the chemical formula being: Be3Al2(SiO3)6. It can occur in many colours ranging from: green, blue, yellow, pink, brown, black or colourless. Beryl, with a hardness of 7.5 on Mohs scale of relative hardness, is quite soft in relation to other valuable minerals such as diamond or corundum. Emerald, by far being the most valuable of the beryl species, has the presence (trace element) of chromium, vanadium or iron which can give it a green, yellow-green or blue-green colour.
The most desired aspect of the emerald is its body colour and how well it interacts with light. Essentially, how vibrant or intense the stone is while maintaining a well- balanced green hue throughout the crystal or stone. Emeralds from Colombia owe their deep pure green hue to the presence of chromium and lack of iron, as iron will cause a more bluish-green hue of colour as seen in Zambian emeralds. The difference in colour can be hard to see but in some instances quite obvious. (figures 12 and 13)
There are subtle differences in the emeralds found from different mines in the Boyacá region and it really comes down to personal opinion on what stones are better, ‘Muzo emeralds tend to be a well-saturated slightly yellowish green, while Chivor emeralds are generally less saturated and more bluish-green’, and from Cozcues, ‘there is no one specific hue or degree of clarity associated with Cozcues emeralds, rather, a variety of hues occur’ Ron Ringsrud (1986). Emeralds are different than other valuable stones because there is a universal acceptance of the presence of inclusions. Of course, if a stone is too heavily included that it compromises the colour, it would not be considered a rare and valuable stone, ‘The disparity between the value of a perfect and of an imperfect emerald is enormous. A faultless emerald is worth as much, or nearly as much, as a ruby, and certainly more than a diamond’ Dr. Max Bauer (1904).
Inclusions can give insight into the growth processes of emerald. Typically, emeralds are moderately to heavily included and can contain: Multi-phase inclusions, fingerprints, growth tubes, fractures, minerals or single crystals such as tourmaline, emerald (within emerald!) or ‘jardin’ (French for garden) which is a term used to describe a mossy or garden-like abundance of inclusions in an emerald (figure 13). Emeralds with high quality colour and no (or very few) inclusions are extremely rare. Colombian emeralds from different mines do however share something in common: the two or three-phase inclusions of a liquid, gas and solid (for example, a halite crystal) or coal-like inclusions of carbonaceous matter. Other minerals which are found in Colombian emeralds include: Calcite, albite, quartz, and pyrite and in rare cases: barite, fluorite and apatite (figures 14-17). These internal features can lead an individual to assume that a particular emerald came from Colombia; however multi-phase inclusions can occur in emeralds from other localities too.
Emeralds can be cut into many shapes such as: oval and round mixed cuts, cushion cuts, cabochons, or even carvings. However, because they are brittle in nature with a hardness of 7.0 - 7.5 and commonly have internal fractures leading to the surface, the emerald cut (figure 13) is usually the safest option for the lapidary because it allows a more stable surface for claws to hold onto (on the 4 corners). Another important thing for a lapidary to consider is ensuring the stone cut has a ‘maximized effect of hue, tone and saturation’, and that, ‘the cutter can affect colour by adjusting an emerald’s proportions and number of facets. The cutter can darken a pale stone with a deep cut, a small table, and fewer facets, or lighten a dark stone with a shallow cut, a large table, and additional facets’ (GIA 2002-2015).
Emerald treatment with oils or resins is a common practice in the industry as it can greatly improve colour and clarity of an emerald, and increase its durability. The value of an emerald can be dictated by whether or not it has been treated and what exactly it has been treated with. There are many methods used in the application of these treatments - as well as the substances themselves - so I will only mention a couple.
Basically, this process involves applying oils or resins to the surface of the emerald that seep into surface-reaching fractures. It is generally accepted for emeralds to be treated with natural oils such as cedar wood oil which are not permanent and do not damage the stone. However, unnatural oils or resins (epoxy or polymer) are also widely used, such as the notorious Opticon. These resins - in unhardened or hardened form - are typically more durable than natural oils, but they can permanently damage an emerald (effectively making initial inclusions worse, or staining the inside of the stone) if it is somehow cleaned with either an ultrasonic, other cleaning liquids or exposure to harsh environments, ‘Fillers add risk by hiding or disguising existing durability problems. There is also the risk involved in cleaning and filling the emerald - and removing damaged fillers’ Mary L. Johnson (2007).
Identifying these treatments can prove to be difficult and the issue is with merchants selling emeralds as ‘untreated’ or lying about the substance that the emerald was treated with. One way to identify Opticon treatment in an emerald is to use appropriate lighting and magnification with a microscope or a 10x loupe, where a distinctive orange flash can be observed (figure 19). Sophisticated lab equipment such as a Fourier Transform Infrared spectrometer (FTIR) or a Raman micro-spectrometer are effective at probing the material and giving definitive results.
Synthetics and Simulants
There are many synthetics and simulants in the marketplace in Colombia, and the rest of the world for that matter. People have been known to sell green glass or plastic claiming it to be emerald. Craftier people have laminated a slice of emerald crystal to a piece of green plastic, or used quartz crystals made to look like emeralds by coring them and filling them with green plastic and attaching them to a shale matrix. The list could go on, but as long as the material ‘looks’ like an emerald, anyone who is desperate and cunning enough will try to sell it to the unknowing customer. Synthetic emeralds fall under the flux-melt or hydrothermal processes, but these aren't exclusive to Colombia.
Trapiche emeralds are an oddity and rarity which can only be found in Colombia. These consist of a central hexagonal prism core, with what appear to be spokes or a radial pattern stretching outwards. This black pattern can be composed of carbonaceous matter or albite which has been trapped inside during the emerald crystals growth.
Colombian emerald prices can range between $10 - $50,000 US per carat, and can far exceed this depending on the stone. It is impossible to deter how much emerald has been mined out of Colombia because of the lack of organisation, infrastructure, changing of hands, smuggling and thievery - to list some examples. There is no question that there was an enormous abundance of emeralds at the mines in Boyacá and only until the past couple of decades has the production declined. Colombia had been the leading emerald producer in the world up until recently.
Relatively recent statistics can give us a fair idea of when Colombian emerald production started to decline dramatically. In 2002 emerald production values were estimated by the Ministry of Mines and Energy of Colombia. The results were: Colombia: 60%, Zambia: 15%, Brazil 12%, Russia 4%, Zimbabwe 3%, Madagascar 3%, Pakistan, Afghanistan, Australia, Tanzania 3%.
Export figures from 2004-2011 supplied by the Colombian Geological Service can also give insight into the decline in production. In 2004, 9 million carats of rough was exported and valued at $1.45 million US, 48 thousand carats of mounted emeralds was exported and valued at $0.99 million US and finally, 0.75 million carats in cut emeralds was exported and valued at $74.8 million US. The total value of emerald exports was at $77 million US.
From 2005-2010 exported rough, mounted and cut emeralds generally declined and the total export value increased. There were some exceptions however. In 2008, the total export value rose to $164.6 million US, the majority of this sum came from 0.58 million carats of cut emerald valued at $162.8 million US. The demand and price per carat exploded this year.
In 2011, 2.95 million carats of rough was exported and valued at $5.67 million US, 26.5 thousand carats of mounted emeralds was exported and valued at $0.43 million US and finally, 0.42 million in cut emeralds was exported valued at $131 million US. The total value of emerald exports was at $137.1 million US
These trends show that the quantity of emeralds exported has declined and the price has risen. This is due to the fact that the mines are becoming exhausted and miners need to dig even deeper into the mountains which requires more sophisticated equipment, formal financing and infrastructure. However, there still is a demand for high quality cut emeralds from Colombia.
In the past several years, Colombia has fallen behind both Brazil and Zambia in emerald production, "Colombia's total emerald output was 2 million carats last year (2014), a decline of 25% from 2013, according to the country's mining agency. Formerly the world's biggest producer of the green gemstones, Colombia has slipped behind Zambia and Brazil in recent years as its aging mines lack investment in new machinery, Oscar Baquero, the head of the country's emerald federation, said in September" Andrew Willis (2015).
The closest I could physically get to the emerald mines in Colombia was by interviewing an emerald merchant going by the alias ‘Emerald Al’. We sat at a cafe for an hour and he gave me very interesting information about the mines, the emeralds and Colombia in general. Since I had talked to him in late 2014 he had been to Bogota three times.
Getting to the mine, he says it was ‘hell to get in, hell to get out, especially in the early days, but not so bad now. Driving through the jungle, anyone going in or coming out was known to either have money on them to buy emeralds or coming out carrying emeralds’ and then he mentioned armed convoys. I can imagine it is not the kind of place the average gem enthusiast would want to visit.
The emerald dealers primarily want cash and certain trusted people can purchase them with cheques. He brushed on the civil wars that took place for 40-60 years where the guerrilla movements fighting against the government used means of violence, kidnapping, money laundering and the majority of their operations were funded by drugs and emerald money. This was part of what is known as the ‘green war’, in which rebel movements, drug cartels and the government forces were fighting over ownership of the emerald mines in Boyacá resulting in thousands of deaths.
An important name to mention is Victor Carranza, also known as the ‘Emerald Tsar’ who died from cancer in 2013 at the age of 77. From the 1980s he ran mines in the Muzo district and controlled up to 40% of the country's emerald business at one point. It was reported that he employed right wing paramilitary troops in order to retain his power. He was also jailed in 1998 and released 4 years later and in 2010 he survived an assassination attempt. Al says: ‘There's a lot of violence in the emerald game’ and I'm not surprised.
Al mentioned the emerald district in Bogota where almost all the emeralds mined from Boyacá end up to be sold and cut. There is an avenue within this emerald district called Avenida Jimenez where you may get swarmed by local emerald dealers, some of which would try to sell you low quality emeralds and synthetics or simulants. He mentioned a large building called the ‘Emerald Trade Centre’ and other buildings filled with emerald cutters and dealers. Al buys most of his emeralds from Bogota but in the past has also bought some stones from workers at the Muzo mine itself. Care needs to be taken when carrying around emeralds or cash, as Al says: ‘There's particular people you don't buy from because they're shifty’.
The Emerald Pipeline
This is an emeralds journey from Boyacá, Colombia to another country: A lowly miner does the physical work who hands the emerald rough to the manager on site, who brings this to the mine owner, or this process is bypassed and it is sold at the gate or brought to the nearby town of Muzo.
Another person buys the ‘pocketed rough’ and brings it with him to Bogota to sell to a friend or relative. The friend or relative cuts the rough and then sells the cut stone to another friend or relative to sell yet again! At this point it has landed into the hands of an emerald dealer or merchant who would sell it to their customer. This could be a jeweller or jewellery store in another country. Then the jeweller or jewellery store sells it to the final customer.
After researching and presenting this information on Colombian emeralds I have become even more fascinated with them and will continue to learn more. I feel that my project is limited considering I have not been to Colombia and experienced the mines and met people there myself. However, because of this very reason, I was driven to learn as much as I could about this topic and have provided a broad scope of information which is all relevant to the emeralds. It is unfortunate that the emeralds can cause people to be violent and greedy which may result in casualties and deaths. Currently the mines need to be updated and the government and experts know this. Although the existing mines are quite exhausted, there may still be a chance that new veins bearing many fine emerald crystals can be discovered, where positive mining companies such as Gemfields may be able to help in building solid infrastructure to at least one of the mines. This will be a difficult and delicate task for outsiders, considering the gruesome history and people in power who may not be open to such change. Despite all this, the fact is: Colombian emerald is a beauty of this earth and its amazing deep green hue is unmatched.
- Jacob Francey FGA
- Jewellery Valuer
- Auckland, New Zealand
- Jewellery Valuers Company Ltd
- Gems / Gemmology (primary)
- Gemmology Students (primary)
- Jul 2020
- 20 mins reading time
- Dale-Chall readability level:
Easily understood by an average College Graduate
- 30 mins speaking time
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