Mark Cole: There was a post in the fluorescent mineral group about sulfur fluorescing a dull green under SW on a piece of calcite from Michigan, and a discussion about this being real fluorescence ensued. I have several pieces of similar material from Italy and had noticed what appeared to be a dull luminescence but thought it was just the aragonite under the sulfur shining through the translucent sulfur - but was never sure. So I took a piece and chipped off a little chunk of sulfur. (For my specimen) the results were conclusive.
I took the chip of sulfur and placed it next to the aragonite as seen in the first picture below. The aragonite fluoresces a beautiful bluish/pink and the sulfur seems to have a dull yellow fluorescence. At the lower left of the specimen is the little chip of pure sulfur I removed from this piece. It still seems to have this same dull fluorescence even though there is no aragonite underneath it. Now to the 2nd pic below....
In this picture I simply removed the aragonite specimen from the camera's field of view. The small chip of sulfur is still there (the arrow is pointing at it). I took the pic with the same exact camera settings and developed it in RAW with the same exact parameters. You simply cannot see the sulfur. My conclusion based on this pic is that the sulfur is both transmitting the fluorescence of the aragonite that is underneath, but also reflecting the luminescence, as seen in the first pic. Without the aragonite in the picture there is nothing to be seen. But - my piece is from Italy, the piece under discussion is from Michigan - could be true fluorescence in that case. No way to tell without some (possibly destructive) experimentation. On to the 3rd pic....
In this third pic I just cranked up the exposure to prove that the chip was still there. If there were a fluorescent rock in this photo (willemite, aragonite, tugtupite, etc) it would be a blinding white because of the overexposure setting of this photograph.
Chris Clemens: The first photos of mine posted to the Nature's Rainbows photo gallery (courtesy of Mark Cole) stimulated much discussion regarding the fluorescence of mineral sulfur. This is the post that Mark refers to above. The photos in that post showed a specimen of sulfur crystals perched on top of a bed of brightly fluorescent calcite. The piece was collected from Maybee, Michigan, a source that was described by Manuel Robbins as producing sulfur that shows weak yellow fluorescence under UV (Robbins, Fluorescence- Gem and Minerals Under Ultraviolet Light, 1994, p. 192). Under short wave UV, the sulfur on my specimen appeared to show a weak yellow/green fluorescent response, consistent with Robbin's description, and very similar to what Mark shows in his photo of Italian aragonite above. Here is the photo of my specimen, taken under short wave UV:
Indeed, the sulfur appears to be fluorescent in this photograph. However, the sulfur is quite translucent. Could it be that the sulfur is simply transmitting the light emitted by the brightly fluorescent calcite? This was the topic of much debate on the page of the Fluorescent Mineral Group. Mark showed that in the case of his Italian aragonite specimen, the apparent fluorescence of the sulfur was in fact an artifact resulting from the translucency of the sulfur allowing the fluorescent light emitted from the aragonite to pass through, conveying the perception that the sulfur itself was fluorescent. In the case of my specimen, I was not willing to chip off a sample of the sulfur to repeat Mark's experiment.
At a recent show, I picked up another sulfur specimen from Maybee, Michigan. On this piece the sulfur crystals sit on top of a brightly fluorescent calcite and celestine druse. Again, under UV the sulfur appears to show a weak yellow/green fluorescent response. Here is a photo of that specimen, taken under long wave UV:
The back side of of this specimen also has limited sulfur coverage, so I was willing to remove a sample for analysis of fluorescent response. I took the sample of sulfur, in the absence of the fluorescent matrix, and checked it for fluorescence under all UV wavelengths. To document the results, I took photographs using the same UV lamp (Way Too Cool, 18 watt) and exposure settings as were used to photograph the intact specimen. The following figure shows the comparative results of this experiment:
The images in the left column show the intact specimen photographed under the specified visible and UV lighting. The right column shows the isolated sulfur sample removed from the specimen, photographed under identical lighting and exposure conditions. These results show that the sulfur sample was not fluorescent under long or short wave UV, as only a dim lamp reflection can be seen.
The results of these experiments, done by Mark and myself, clearly show that in the cases of our specimens, the sulfur was not fluorescent, but they certainly do not disprove the existence of fluorescent sulfur. However, this work dose illustrate the potential for certain transparent or translucent minerals to convey the appearance of fluorescence if located within close proximity to other, brightly fluorescent, species. Therefore, the search for the elusive fluorescent sulfur continues...
(Added by M Cole:) P. Tauger on the FB Group posted a pic of sulfur from an unknown locality that he acquired when he first started collecting. No idea where it's from, but it sure looks like the sulfur is fluorescent. Anybody with information please shoot me an email. Pic below: