Update of GRS "Old Mine/ Muzo Green” emerald report policy

Lucerne, Switzerland [updated 6 November 2017] – The 1st International Emerald Symposium held in Bogotá, Colombia, October 13-15, 2015 brought together leading members of the gem and jewelry trade from around the world. There, GRS presented its proprietary color-grading concept for emeralds called GRS type “Muzo green” which identifies stones with exceptional color saturation and hue.

Gathering helpful feedback from symposium attendees together with fruitful dialogue in which Dr. Peretti and expert panel members participated; a slight modification to the current Muzo Green appendices was created which reflects a more neutral phraseology. The small but valuable adjustment helps to clarify that the various emerald mines in Colombia can produce this very fine and strongly saturated color.

Geologically speaking, the emerald mines of the western part of the emerald mining areas in Colombia are found in the so-called “Muzo Rock Formation”. The name Muzo has been therefore already been used in the scientific world to describe the rock formations containing emeralds in Colombia. In continuation of this tradition, GRS chose this name (Muzo) to describe the ‘best color’ for Colombian emeralds.

Below is the revised version of the emerald report appendix:

Front-page of GRS report with "Old Mine / Muzo Green" appendix.
"Old Mine / Muzo Green" appendix.

More on about "Old Mine / Muzo Green Appendix"


This color term describes the finest color range found in emeralds of Colombian origin. GRS introduced the special “Old Mine / Muzo Green Appendix” onto the gemstone market in 2015, creating a market standard for the trade, auction houses and consumers. “Muzo is the most famous of Colombia’s emerald mines. It has produced stones of matchless beauty for more than a thousand years. The rare, fine, saturated green crystals sometimes found there are the yardstick by which all other emeralds are judged.”


Our “Old Mine / Muzo Green Appendix” describes emerald originating from Colombia with a strongly saturated vivid green color range. Qualifying emeralds receive an appendix to the GRS gemstone report with comments as follows:

“This vividly saturated emerald of 8.35 ct is reminiscent in hue of the varieties displaying the legendary colors found in the world renowned Muzo mines. They are formally described as “Muzo Green” (*) and commonly known in the trade as “Old Mine” emeralds.” 

*This appendix indicates the specific quality and color for emeralds from various Colombian mines; however, it does not specify from which particular mine they were found. 

Emeralds qualifying for the “Old Mine / Muzo Green Appendix” title can be found from a variety of Colombian emerald mines such as Muzo, Coscuez, Chivor or Cunas. 

The “Old Mine / Muzo Green Appendix” title is not granted for emeralds with:

  • Dominant quality issues such as apparent color zoning, windowing or disturbing inclusions
  • Low quality minor to moderate and all moderate treatment grades
  • Surface cavity fillings
  • Irradiation, coating or other color-modifying treatments
  • Obvious and disturbing non-enhanced clarity features
Colombian emerald ring 5.70 ct, no indication of clarity enhancement with “Old Mine / Muzo Green Appendix”. GRS Collection. GRS2016-028509.


The first international auction house publication to use the GRS term “Muzo green” was in 2015 (Tiancheng International Auctioneer | Hong Kong Autumn Auction 2015 | Lot Nr. 190 | GRS Number GRS2014-103592).


The main cause for color in emerald is chromium (Cr) and vanadium (V). “Old Mine / Muzo Green Appendix” emeralds are rich in their chemical concentrations and thus have a comparatively high content of Cr and V when compared to emeralds from most other localities. Colombian emeralds mostly contain distinct and typical three phase inclusions consisting of tiny crystals and a gas bubble in liquid.

Vividly saturated Colombian emerald displaying the legendary colors found in the world renowned Muzo mines.
A 3-phase (liquid, solid, vapor) inclusion typically found in a Colombian emeralds.

Citations related to the topic

"Muzo is the most famous of Colombia’s emerald mines. It has produced stones of matchless beauty for more than a thousand years. The rare, fine, saturated green crystals sometimes found there are the yardstick by which all other emeralds are judged."

Sauer, J.R., 1982. Emeralds Around The World. 1st ed. Rio de Janeiro: J.R. Sauer.
This citation can also be found in Ringsrud, R., 2009. Emeralds, A Passionate Guide. 1st ed. Page 97: R. Ringsrud.

"For Colombian emeralds, the term Muzo green is often awarded to stones which have the desirable grass green or lime-jello shade. Muzo green emeralds don’t actually have to be from Muzo."

Morgan, D, 2007. Satan’s Crown to the Holy Grail: Emeralds in Myth, Magic, and History. 1st ed. Praeger.

Jewellery News Asia. 2010. The magical ‘green fire’ of Muzo Emeralds. [ONLINE] Available at: [Accessed 28 October 15].

"The Mogul emperors and the Maharajahs were so enamoured with emeralds that they had adorned their crowns and embellished their thrones with this gemstone. Their emerald collection was so extensive that people thought India had a secret mine centuries ago. Those emeralds actually came from Muzo."

Mr. Gilles Haumont

Gemstone expert Gary Roskin, host of the Roskin Gem News Report and adjunct instructor of gemmology at The Fashion Institute of Technology at the State University of New York, said Muzo emeralds are known for their depth of colour and their richness of pure green with a hint of blue or yellow. 

“They can be found in large sizes and with wonderful transparency. Colour, which is the most important factor, size and transparency place Muzo on the mountain’s peak for the world’s finest emeralds,” Mr Roskin said. “Probably the most incredible nature of Muzo is that it not only produces the finest quality emerald in the world, it has been doing so since the Spaniards came to Colombia several hundred years ago, and possibly as far back as the 1500s.” “There are magnificent emeralds from other parts of the world, most notably Pakistan and Afghanistan; but Colombia, and Muzo in particular, because of its unique geologic formation, produces them in a consistent stream."

Further readings related to the topic

Modern Jewelery/David Federman. 2015. Muzo Emerald. [ONLINE] Available at: [Accessed 28 October 15].


Poly Auction Hong Kong. 2015. A SET OF EMERALD AND DIAMOND JEWELLERY, BY WILLIAM GOLDBERG. [ONLINE] Available at: [Accessed 28 October 15].

Geo Heavens Minerals. 2014. Emeralds from Colombia. [ONLINE] Available at: [Accessed 28 October 15].

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