by Marc Gering
Emeralds: this queen of gemstones quite rightfully has a long and lustrous history due to her beautiful chrome green color, deep vibrant glow, and rich brilliance. Artifacts date back centuries through ancient Rome and Egypt to Pre-Columbian works of the New World. On-line one can find some of the romantic history of one of the earliest emerald mines known at Sikait (13 Feb 2007). Looking at these pictures one gets the feeling of antiquity and history these gorgeous gems have and of the hardships and difficulties endured to gain just a precious few of them.
Through out history this magnificent stone shines forth from the Egyptians, like Cleopatra who had adorn herself with these priceless stones and gave engraved gems to special friends; to the Romans Nero was reputed to have watched coliseum games through an emerald lens, (although there is question on whether this description is accurate:) through the Pre-Columbian Indians of Central and South America with the unique and beautifully carved Emerald Man (13 Feb 2007).
Even our fiction reflects our fascination with this spectacular gemstone the Emerald City of the Oz books for example. There are plenty of books and articles describing the beauty of the emerald, from the rich green tones, to the jardin, (garden,) inclusions that often fill these stones, (and make identifying the origin simple,) to the cutting properties of this awesome form of the mineral beryl. But there is not too much information on this rarest form of emerald: the Trapiche Emerald.
Ok, where does the name come from? tra·pi·che (de azúcar) sugar mill.
More specifically we can find It is named for the trapiche, a grinding wheel used to process sugarcane in the region2 This is a good name for these unique gems. In the figures below we can see the spoked structure in these gemstones.
In Figure 1, notice the hexagonal core, this shape is typical for the growth of emeralds. Figure 2 shows a Trapiche emerald with no central core. There was some belief that Trapiche from one mining area displayed the central core and those from another did not have it. We have seen pictures on the web stating they from both localities showing with and without the core.
Both forms are lovely gems.
We can let our imagination run free when we gaze upon these precious gems. In the stone below I see a spider.
And in this gem I see a moth.
These wonderful emeralds can get very large and weigh several grams:
(These two photographs are courtesy of Mr. Farooq Hashmi, Intimate Gems)
As for the material forming the dividers, we read: A TRAPICHE is the result of the growth of an Emerald Crystal with the darkened impurity of lutite. As the Crystal grows in its normal six-sided shape, the darker lutite is pushed to the center of the Crystal and then radiates out in the six directions of the corners of the Crystal. A 1970, analysis of MUZO´s trapiche emerald by Nassau and Jackson, found that the principal coloring agent was vanadium.3 and Trapiche Emerald's are formed when black carbon impurities fill in at the emerald crystal junction which forms a radial pattern with a six-pointed star effect. In some trapiche emeralds, inclusions consisting of albite, quartz, and a carbonaceous material outline a hexagonal beryl core, and they extend from it in spokes that divide the surrounding emerald material into six trapezoidal sectors. Often, the hexagonal beryl center is transparent and colorless, or it can be green.4
This is not a case of asterism, but rather of crystal growth. So what is the mechanism that caused the creation of these beautiful and unique gems to form in this unique fashion? We have found the following: The structure and mechanism of growth of these crystals, which have been found at the Pena Blanca mine near Muzo, Colombia, have been studied by Nassau and Jackson, who reported their results in a short paper in the Lapidary Journal, and in a more detailed report in the American Mineralogist. Briefly, their proposed mechanism for the formation of trapiche emeralds is as follows: First, the central, tapered core grows under hydrothermal conditions. Second, growth may slow or even stop for a while. Next, growth conditions change again, and both emerald and albite are formed. However, the hexagonal prism faces of the core crystal are able to maintain their uniform growth, producing pure emerald, while areas growing from the edges between prism faces are not, and are filled by albite. This results in six sectors of clear emerald, and six of predominantly albite and minor emerald. Thus, the central core and the six surrounding sectors of a trapiche emerald comprise a single, untwinned crystal.5
It was long believed that these beautiful gems only came from Columbia, These rare Emeralds are only found in Colombia occurring at Muzo and Penas Blancas mines.4 However we have found a reference to another location: A large grayish green trapiche beryl,6 weighing 13.74 carats from Madagascar has been reported in Gems & Gemology. Information is very scarce on Trapiches from this area.
A quick word on treatments and enhancements is in order at this point: visitors to the actual mines recently report obviously treated material being sold as natural. Treatment takes many forms, the most common is oil or epoxy impregnation of cracks, (this type of treatment is typical for most of the emeralds on the market.) For a dissertation of the GIA approach for emerald grading see: Gems and Gemology, Winter 1999, Classifying Emerald Clarity Enhancement at the GIA Gem Trade Laboratory - by Shane F. McClure, Thomas M. Moses, Maha Tannous, and John I. Koivula, p.176-p.185.
In conclusion, if you are looking for a unique, beautiful, rare and wondrous gemstone the Trapiche Emerald truly fits the bill!
References: All sites visited on 22 Dec 2013
- Author Unknown. "...and trapiche beryl." Gems & Gemology Summer (1998): pgs 137-138
- Marc Gering, Jazzan Jewels (except where noted)