LUCAS SP Database vs. pure mineral Gypsum

In order to find if the soil has traces of a certain mineral, it is useful to overplot our soil samples (in this case the soil Spanish samples included in the LUCAS database, with the pure mineral spectrum  (in this case Gypsum). We must  overplot them with the same math treatment and in the same scale. I do it, in this case, with the spectra treated with the SG second derivative.

 In red is the pure gypsum mineral and in grey samples in the soil database.  As we can see some of the bands match, so we can be quite sure that there are some samples in the database with gypsum content to certain levels.

Second derivative is quite helpfull to find these matches. If we do it, for example with SNV+Detrend, some of the bands are hiden by other samples and the assumption that there are samples with gypsum is less clear.