Coupled SEM-microRaman system: A powerful tool to characterize a micrometric aluminum-phosphate-sulfate (APS)

Here we used a coupling device between a scanning electron microscope (SEM) and a microRaman spectrometer to analyze micrometric aluminum-phosphate-sulfate (APS) occurring in a complex geological system. The capability to get BSE contrast, WDS elemental mapping and Raman data on tiny grains, allowed new structural insight for an APS with a high PO4/SO4 ratio and capability to distinguish compounds with complex variable compositions between the minerals alunite (KAl3(SO4)2(OH)6) and crandrallite (Ca(PO4)2(OH)5⋅H2O).