CompuServe Messages

Hi, Doug– >> Hydrocarbon inclusions in minerals often fluoresce a bright yellowish-white…<< I'm beginning to think this might be the right tree to be barking up. I checked a couple of entries in Deer, Howie and Zussman, and found the following under "Montmorillonite Group (smectites)": "Various organic molecules can also be accomodated in inter-layer spaces…" The fact that the samples came from within a hydrocarbon-rich shale supports this theory. I was unable to get any kind of solvent cut from the sample, so if inter-layer hydrocarbons are indeed the cause of the fluorescence, they must be pretty well bound into the structure. >> Calcite and aragonite flouresce bright yellow-white… – any fizz? << Nope, no fizz, even on heating in 10% HCl. The only reaction at all was that the HCl starting taking on a yellowish tinge in cold HCl after about a minute, which usually indicates iron. Submicroscopic pyrite could account for the greenish grey colour of the rock. >> I have one casual indication of a modest white response from kaolinite. << Most of the kaolinite I run into doesn't fluoresce at all, at least not in long-wave. >> Are we talking radioactive like granite, or radioactive like high-grade uranium ore here? << Radioactive like granite. >> Can you describe the brightness and precise color in terms of any "commonplace" (to fluorescent colors) mineral specimens? << Sorry, I don't have any reference material to compare it with, not being a fluorescent mineral collector myself. The colour of the yellow is more green than orange. >> I am surprised you use only longwave UV… << Longwave UV is the standard for oil-industry use in describing the fluorescence colour of oil staining and solvent cuts (the API gravity of various oils is estimated using fluorescence). This is the only application I have for fluoroscopy, so my longwave "UV box" is all I have. Since reading your response, I did a few more experiments that shed some more light on the subject (no pun intended 🙂 Heating chips of the material produces no noticeable hydrocarbon odor, although a slight H2S odor was noted, which might be accounted for by pyrite. As well, the fluorescence was noticeably reduced. Holding the chips in an open flame (alcohol) for a few seconds causes them to turn darker grey (I don't think due to soot), and fluorescence is lost completely. It seems to me that these facts may also point to interlayer hydrocarbons in smectites. The darker colour and loss of fluorescence could be explained by oxidation of the interlayer molecules to carbon. The main reason I didn't initially consider that hydrocarbons were responsible was the fact that the surrounding organic shale, while distinctly oily, gave a good cut but had no to very dull brown fluorescence. Perhaps the smectites preferentially adsorb lighter fraction (condensate/gasoline range) hydrocarbons. Or, perhaps being structurally integrated into the montmorillonite layers somehow enhances the fluorescence. I also tried adding water to heated chips, to see if their swelling properties were enhanced, perhaps by driving off some of the hydrocarbons, thus making room for water: no swelling was observed. (Heating smectites too much causes them to lose the ability to adsorb water, but I tried with samples heated to varying degrees, with no apparent difference.) I guess another test would be to get some dehydrated bentonite and soak it in gasoline/varsol/oil and see what the results are. >> If you want to send me a sample..<< If you still want a sample, you can E-mail me your address, and I'll send some down to you to check. Thanks for the discussion. Howard.