For my M.Sc im working on material that consists of sedimentary pyrite concretions that are polished into slabs for reflective optical microscopy. Under microscope I only see plain fields of pyrite and I can not distinguish between fine grained pyrite in the core and radiating crystals that are enclosing it. It seems like a thin film of pyrite from polishing is smeared on the surface of the polished section.
I read in several publications that treating the surface of concretions with nitric acid may reveal texture in that kind of material.
Different authors are suggesting different procedures using nitric acid, and I would be most grateful if someone could give me some advice on that since material is scarce.
Thank you very much in advance for you help!
Best regards,
Aleš Šoster
Dear Mr. Šoster,
etching of polished sections is a classical method in ore microscopy and may indeed be a good tool to elucidate the textures of ore minerals, particularly being intergrown with other minerals of the same kind or chemically similar. HNO3 be it diluted or concentrated gives a moderate response in form of a brownish tint. There is also some effervescence. Permanganate dissolved in H2SO4 is better and more meaningful. As you revealed in your question that the amount of sample is scarce I suggest taking from a collection some pyrite which is normally a "jack of all trades" in these samples and perform some trials. This is the way I tried to tackle a problem like that.
Viel Erfolg
Harald G. Dill
Dear Ales, Prof. Dill suggestions are probably helpful. You can also use hydrochloric acid in some circumstances. May be suitable to your case (?). See the paper provided. Best Regards, Anicet
I normally put concentrated nitric acid in a 30ml dropper bottle. Put one or more drops of the acid on polished thin section/block, where the pyrite grains of interested are. Wait for ~15 seconds, then wipe the acid off. Clean the surface with ethanol or water (ethanol evaporates faster) and Kimwipe. Cheers, Zhaoshan
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