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Genthelvite - rare from Sterling Hill, NJ

Genthelvite (with a hard "G") is not uncommon throughout the world but it is very rare at the Sterling Hill Zinc Mine in Ogdensberg, NJ. Not discovered at Sterling Hill until 2002, where it was found in a narrow trench dug near the connecting path between the Passaic and Noble pits at the mine. A pale green in daylight, genthelvite glows a distinct brilliant green different from the surrounding willemite. In fact, that's how I found that I had some. The assemblage seen here is new for genthelvite. Normally found in dark-colored amphibole, the matrix here is good old calcite, willemite, franklinite, a mix that at least I refer to as, "cookie dough". While searching for just such a piece through my reserves of this assemblage for a customer, I saw three, small areas, roughly 3mm each, glowing their brains out that were acting as if they were not willemite. For one thing, they glowed brilliantly under 365nm UV, but almost not at all under SW UV. Secondly, the color was a pure green without the yellow component that gives willemite it's characteristic hue. After researching, I suspected genthelvite and got the rock to Dr. Earl Verbeek at Sterling Hill to analyze it using the Raman IR spectrometer at his disposal. The result was definitive. Genthelvite all the way! See Dr. Verbeek's article in the FOMS publication, The Picking Table, Fall 2017 for his detailed report on this specimen.

I collected this rock at Sterling Hill in the mine run dump during the Spring 2015 night dig from SH material dumped there from elsewhere on the property. I had this rock in my possession for over a year before I happened to discover the genthelvite in the manner described. Do you have any? It's easy to mistake it for willemite but just as easy to check for it when you know what to look for. Hyper-bright under 365nm, next-to-nothing under SW (though genthelvite from Franklin responds in the opposite way but not as brightly under LW).

Photos are: #1: Largest grain under 365nm close-up, #2: Under365nm - shows the difference between genthelvite and willemite, #3: Under 395nm + yellow filter, shows how bright the genthelvite remains and is distinct from the willemite's lesser reaction, #4: Under 254nm SW, there's almost no reaction at all, #5: Specimen in white light.

 

 

 

 

 

 

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