Bright Green Enstatite from Tanzania
Recently, I was honored to be asked to co-author an article for the Journal of Gemmology, one of the most highly-respected gemological publications in the world. I had the good fortune to stumble upon a previously unreported occurrence of the gem Enstatite while buying rough at the Tucson Gem Shows in 2019. The rough was presented to me as something completely different by the dealer, but it just didn't seem right. Here's the story of how this discovery was made, and how it went from my rough box to the Journal.
Enstatite is a gem that you might not have heard of, and for a pretty good reason. It is typically not found in attractive colors. Most examples you'll see online are a very drab brown. It is also VERY challenging to facet, as it has very delicate cleavage that can result in the stone spontaneously cracking/cleaving during the cutting process.
During the 2019 Tucson Gem Show, I was looking through the offerings of Vter Young, a friend and gem dealer that I have worked with numerous times. He had a bowl of what was purported to be sphene. The color and appearance of the pieces did indeed seem to be consistent with sphene, right down to the bright chartreuse color. However, when I louped the rough, the characteristic strong birefringence/doubling that should have been seen was conspicuously absent. Suspecting that it might be peridot instead, I asked Vter if he would mind if I took some of the material for further analysis.
I took the rough over to the AGTA booth of Magilabs, to my friends Alberto Scarani and Mikko Astrom, for a quick scan on the GemmoRaman spectrometer that they had set up for demonstration purposes at the show. To our surprise, the initial result indicated not peridot, but enstatite!
Upon return from the show, I prepped a piece of the material for further analysis by grinding and polishing a flat surface to remove any contaminants that might've influenced the initial test. The piece was then placed on a refractometer to determine the refractive index and birefringence, and was also analyzed by Raman spectroscopy using JL White Fine Gemstones' in-house GemmoRaman spectrometer. All of these results validated the initial indication of enstatite!
While I was able to find some very old published references to bright green as a possible color of enstatite, there have apparently been no instances of such a brightly colored material in decades. After learning of this find, The Journal of Gemmology expressed interest in covering this material and arranged for us to send a sample of the rough gem to Dr. George Rossman of the California Institute of Technology for further advanced analysis (EDXRF, FTIR).
Over the course of the latter months of 2019, the article came together and was finally published at the end of the year in Volume 36, No. 8 of the Journal. Covered in the article are the results of all the analytical tests performed, including RI / birefringence, Vis/NIR spectra, quantification of the trace element impurities, and more. For all the details on this interesting material, pick up a copy of the Journal of Gemmology!
By the way, are you curious about why this material looks so very different from other enstatite? Dr. Rossman discovered that the unusually bright color was likely due to the presence of a high concentration of vanadium (as V3+) in the crystal lattice.
This illustrates perfectly why I so enjoy our annual trip to the desert for the Tucson Shows - you truly never know what you will find!