SEM Laboratory

(energy dispersive spectrometry, EDS)

The chemistry of the samples is analysed with two energy dispersive spectrometers (EDS). These detectors allow for the simultaneous measurement of major and minor elements in concentrations larger than c. 0.5 wt%. The technique can be applied on points, selected areas or for element mapping.

^{Point analysis with EDS detectors, showing the chemistry of individual minerals. The spectrum can be quantified. (click on the picture to view it in full size)} 

 ^{Example of element mapping with EDS software. Individual mineral maps can be combined.}

(Zeiss Mineralogy software)

Mineralogy of polished sections can be automatically categorised by the Zeiss Mineralogic software. Before analysis and classification of minerals, the mineral library for the analysis needs to be updated by a geologist to match the exact mineral composition for the samples in the project. During analysis, the software creates a false-coloured image based on the underlying Back-scattered electron image and the interpretation of chemical analyses (EDS) for each pixel of the image. The software includes options for mining, like liberation and interlocking analyses, and reservoir analyses, like porosity measurements.

^{Example of an element map showing two types of pyroxene (green and wine-red), ilmenite (orange) and olivine (pink) in plagioclase (blue). Width of view: ca. 8 mm. Pixel size 10 µm.}

The same software can also be used for particle analysis (Computer-controlled scanning electron microscopy, CCSEM). Here, the major and minor element chemistry, grain morphology, liberation, association and locking parameters can be determined on an individual grain basis. The technique can be applied to loose grains or heavy minerals in epoxy mounts and is often applied for provenance, mining and exploration studies.

^{Automated particle analysis applying the CCSEM technique with the Zeiss Mineralogic software. The mineral classification is per particle, allowing for a faster analysis of the sample.}

(Secondary electrons, SE)

With the secondary electron detectors, 3D images of structures, topography and relief of i.e., minerals, fossils, porosity, and mineral overgrowths can be made. The SEM has two SE detectors (for high vacuum and variable pressure conditions) that give birds’ eye view of the sample, and an inLense detector that views the sample exactly from above.

 
 

^{Coccolith microfossil in porous chalk. Image taken with the InLense SE detector (view from above).}

^{Biotite grain in granite rock. Image taken with the variable pressure SE detector.}

(Backscattered electrons, BSE)

The SEM’s back-scatter detector provides an image of the sample’s surface, based on the average atomic number and density of the sample. The technique is usually applied on polish sections.

^{Two material contrast images made with the SEM’s back-scatter detector.}

(growth information, CL)

This imaging technique shows variations in trace element composition or in the temperature during crystallization. It can be applied to image zircons, apatites, diagenetic overgrowths in silicates and carbonates, healed fault zones, ore formations and other cases where growth zonations are expected.

^{Sandstones consisting mainly of quartz grains with quartz overgrowths, which are recognised in cathodoluminescence by a darker grey rim than the core detrital grain. A. Backscattered Electrons, B: cathodoluminescence.}

^{Internal zonation in zircon minerals, revealed by cathodoluminescence.} 

(Electron backscatter diffraction, EBSD)

The electron backscatter diffraction detector (EBSD) can be use to analyse the crystallographic orientation of minerals in samples. The method is for example applied to study preferred orientations, strain in shear zones, material defects, and preferred directional growth on mineral surfaces. The method requires a final polishing step before analysis.

^{Orientation of quartz grains in a sheared pegmatite analysed with EBSD.}