The Mineral Composition and Grain Distribution of Difflugia Testate Amoebae: Through SEM-BEX Mapping and Software-Based Mineral Identification

We tested a scanning electron microscope equipped with the newly developed Unity-BEX detector (SEM-BEX) system to study thirty-nine samples of the testate amoeba Difflugia. This produces fast single-scan backscattered (BSE) and combined elemental X-ray maps of selected areas, resulting in high-resolution data-rich composite colour X-ray and combined BSE maps. Using a suitably user-defined elemental X-ray colour palette, minerals such as orthoclase, albite, quartz and mica were highlighted in blue, purple, magenta and green, respectively. Imaging was faster than comparable standard energy dispersive X-ray (EDX) analysis, of high quality, and did not suffer from problems associated with the analysis of rough surfaces by EDX, such as shadowing effects or working distance versus X-ray yield artifacts. In addition, we utilised the AZtecMatch v.6.1 software package to test its utility in identifying the mineral phases present on the Difflugia tests. Significantly, it was able to identify many minerals present but would require some further development due to the small size/thinness of many of the minerals analysed. The latter would also be further improved by the development of a bespoke mineral library based on actual collected X-ray data rather than based simply on stoichiometry. The investigation illustrates that in the case of the current material, minerals are preferentially selected and arranged on the test based upon their mineralogy and size, and likely upon inherent properties such as structural strength/flexibility and specific gravity. As with previous studies, mineral usage is ultimately controlled by source availability and therefore may be of limited taxonomic significance, although of value in areas such as palaeoenvironmental reconstruction.