Dear Mr. Shan,

with some caveats, your spectra point to gypsum/anhydrite and kaolinite-group minerals, both of which herald a secondary acidic environment and oxidizing conditions. It is a local alteration spot. There a relics of mica and feldspar still present

Kind regards

H.G.Dill

Dear Mr. Shan,

with some caveats, your spectra point to gypsum/anhydrite and kaolinite-group minerals, both of which herald a secondary acidic environment and oxidizing conditions. It is a local alteration spot. There a relics of mica and feldspar still present

Kind regards

H.G.Dill

Hi, I suggest to separate phases if possible.

I made good experience in the past with the combination of XRD and XRF plus stoichiometric calculations (if necessary) for the fractions. At least, for two phases it should work quite well (with mixed layer minerals it might be difficult or impossible).

If you got a certain amount of e.g. SO4 .... left in your calculations, then you might have overlooked another mineral phase. That often happens due to the detection limit of XRD or due to overlapping of peaks in the XRD-diagram.

Microprobe might be another sophisicated method to track down the culprits but should be on the end of the analytic chain because of the high effort and costs.

Best

Mario Wipki