I acquired a Raman spectrum of coquimbite. After I increase the laser power I got a photochemical alteration product, which has the main bands at 1125, 1101, 1083 (triply degenerate). For now, I think that peaks are due to the three different (SO4)2- groups, but I'm not absolutely sure (and also what the mineral is), because in that region there are also high intensity peaks of (CO3)2- group (which is less plausible). See the attachments for the Raman spectrum (.txt format). CrystalSleuth didn't help me to figure out what mineral is, but I think that are some proprietary library database which can find what is that unknown compound. I want to find a solution without XRD, EMPA, or something similar.
You probably know the RRUFF database? See here: http://rruff.info/Coquimbite/R070666
I'd guess that you have heated the sample enough to drive out some of the water content but that you are right and you still have the SO_4 groups. So I would look for other Fe - SO_4 phases. Good luck!
Yes, I know it. As I mentioned, I already used CrystalSleuth which have more or less all Raman spectra from RRUFF database. I also tried all Fe(II) and Fe(III) sulphates with no luck.
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