I’m really enjoying all of the discussion about analyzing various materials with XRF.? I’m quite impressed with the resolution and detail that some of you are obtaining using your ‘amateur’ in-home laboratories.??? I use the term “amateur” lightly – you put the efforts of my past experience in a chemistry laboratory at a nuclear power plant to shame.? Granted, our objective was to analyze for very specific elements of interest, primarily zinc and cobalt, and maybe iron and chromium as well.? We had our XRF set up in a very simplistic manner of push-button, get-banana.? We never strayed from any elements outside of an atomic number Z-range of 24 to 30.

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Anyway, back to my main point of discussion.? I’ve always been a rockhound, and can’t resist picking up something of interest.? Last year I snagged a couple of pieces of some greenish-gray cobble stone that had some white veins of calcite running through it.? On a lark, when it got dark, I shined my Convoy S2+ UV-LED flashlight on the stone.? I wasn’t surprised to see some red fluorescence in the calcite, but was surprised by a relatively bright red phosphorescence that lasted for a few tenths of a second.? What I found even more perplexing is that this phenomenon only seemed to be evident when the stone was illuminated with the Convoy UV flashlight.? I tried getting fluorescence excitation with a combination longwave-shortwave Model UVSL-15 Mineralight (longwave 365 nm, shortwave 254 nm) as well as a dedicated longwave Model UVL-56 Blak-Ray lamp (366 nm).? ?Surprisingly, I didn’t get any appreciable fluorescence, and no phosphorescence, from either of these mercury-vapor based lamps.? Only the LED-based flashlight seemed to elicit the phosphorescence.

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Now for my question:? Would any of you fine gentlemen want to exercise the quest for knowledge to analyze some of this mystery calcite for trace element content to ascertain what might be leading to the phosphorescence?? Being calcite, one would expect Calcium, Sulphur, and Oxygen, but there must be some trace element (rare earth??) that is contributing to the fluorescence and/or phosphorescence?? I went back to the parking lot where the crushed cobble had been placed, and maybe only about a quarter of the cobbles I collected exhibited fluorescence/phosphorescence.? I was able to find several chunks of the ‘pure’ calcite (no green-gray matrix), and it too showed about a 25% to 30% of the number of pieces exhibiting fluorescence.? All of the stone looked similar and probably came form the same quarry, but only a fraction of it showed any fluorescence/phosphorescence.

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Any takers?? I’d be happy to drop a chunk or two of the “mystery” calcite in the mail to anyone who might want to take a crack at running an XRF to look for anything unusual.? Drop me an email if you’re interested.

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Thanks, and keep up the great work!

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Ken Sejkora, WB0OCV

East Falmouth, MA

Email: kjsejkora@...

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