Student Research Projects
Applicability of the SEM and EDS Systems in Mineral Identification
|Student||Meredith Avery, ‘13|
|Department||Earth and Environmental Sciences|
|Course||EES 489: Research in Natural Sciences|
The purpose of our study was to assess the utility and limitations of the Hitachi S-3400N Variable Pressure SEM and the Oxford Instrument’s AZtec program for Energy Dispersive Spectroscopy (EDS) analysis for mineral identification. Using thin slices of rock, rough “natural” samples, and powdered mineral glazes from a previous study, we generated images, compositional spectra, and elemental maps of samples of known and unknown composition. We used chemical analysis to determine the stoichiometry and thus, the mineral from the compounds. We also compared the spectra of our samples to published spectra of known minerals. We know that the SEM cannot detect light elements such as lithium, nor can it distinguish between polymorphs; however, in some cases we were able to look at the crystal structure and cleavage of the sample in order to aid in identification. Advantages of using a combination SEM and EDS system include the ability to identify opaque minerals, the ability to identify mixtures of minerals in rocks, and the ease and lack of expense of sample preparation. Thin section microscopy is limited by the degree of transparency of the thin section and cannot identify opaque minerals. Mineral identification by x-ray diffraction is restricted to pure samples, but it can identify different polymorphs of a mineral. The EDS compositional analysis also allows for the determination of atomic ratios in solid solution series, for example Mg to Fe ratios in olivine, something the other methods cannot do.