Petrology & Mineralogy

Petrology & Mineralogy are focused on the study of solid rocks and minerals. Most of these materials show a wide range of mineral species and very fine structures. Identification of the individual minerals is crucial for both branches. Scanning electron microscopy and microanalysis offer solutions for this problem. They provide information about the morphology in addition to the chemistry of individual grains.
The study of mineralogical and petrographic samples using scanning electron microscopy is now routine in geological research. Similar to optical microscopy but with a much higher resolution, electron microscopy reveals detailed textural relationships between the mineral grains. Its analytical capability has a much wider potential because the interaction between the electron beam and solid matter create several very useful output emissions. Among the most important emissions are backscattered electrons (BSE), secondary electrons (SE), characteristic X-rays and light photons.
  • The intensity of the Backscattered Electrons is directly proportional to the average atomic number of the observed phases and is used for imaging, distinguishing individual mineral grains and identifying zones of discrete phases. The contrast resolution can discriminate differences as low as about 0.1 atomic number. The backscattered electron signal enables the user to track zonation in mineral phases and to find optimal analysis points. Similarly, it can be used to visualize and locate specific phases containing heavy elements. This is especially important in searching for very rare, but very valuable, phases that generally form small grains e.g. gold and platinum group minerals. Differences in the BSE intensity can also be used to identify variable orientation of individual crystals of aggregates.
  • Secondary Electrons are typically used to observe the morphology of three dimensional samples. They are formed closer to the surface than BSE, have high spatial resolution, a large depth of field and they are less sensitive to differences in the atomic number of the material.
  • Characteristic X-rays are the most important output of the electron beam – solid matter interaction as they are used to identify the phases based on their chemical composition. This capability can be used for interactive qualitative assessment but most importantly for quantitative analysis. Special third party detectors compatible with the whole portfolio of TESCAN microscopes are used for this purpose.
  • Light Photons are also a useful product of the electron beam – sample interaction. This phenomenon is known as cathodoluminescence (CL) and produces many different luminescent phases among minerals. Many mineral species differ by the colour of the light emission. The colour CL can be used to distinguish different common rock-forming minerals e.g. feldspars or carbonates. CL is also very sensitive to differences in trace element composition and structural order of some minerals. These effects can be observed using panchromatic (black and white) or colour CL detectors. TESCAN manufactures panchromatic detectors and a four channel combined panchromatic and colour detector – Rainbow CL. A combined solution for simultaneous acquisition of BSE and CL images is also available.
Petrology & Mineralogy
Dendritic crystals of native silver

Related Application Notes

Cathodoluminescence analysis of zircons
Zircons (ZrSiO4) are ubiquitous in the crust of Earth and are a common accessory to trace mineral constituent of most granite and felsic igneous rocks. Zircons have low solubility in most melt and fluid compositions and can survive geological processes such as erosion, transport, or high-grade metamorphism. This makes zircon one of the most important minerals for geochronology. Different types of zircon domains are identified by CL imaging and U-Pb dating is then used to determine ages of different zones within the crystal. This helps to recognize various geological processes recorded during the history of the grain.
pdf – 1.8 MB
Cathodoluminescence imaging of mineralogical samples
Cathodoluminescence (CL) - light emission produced by electron beam - reveals information about material composition and structure that often cannot be obtained by other methods. In geosciences, optical cathodoluminescence became a standard technique. With the development of scanning electron microscopes, SEM-CL is gaining in popularity. In comparison with optical CL microscopes, where the sample is irradiated with stationary unfocussed electron beam, SEM-based CL imaging achieves much better resolution and it can be combined in situ with other analytical methods.
pdf – 3.9 MB
Characterization of Platinum Group Minerals
The platinum-group metals (PGM) consists of six elements – platinum, palladium, rhodium, iridium, ruthenium and osmium. Chemical inertness, oxidation-resistance, biocompatibility, high melting temperature, good conductivity and electronic and catalytic properties are unique properties that make PGM irreplaceable starting material in many specific applications. The deposits in the Norilsk-Talnakh region of Northern Russia are the largest nickel-copper-palladium deposits in the world and, the intensive mining activity in this region, positions Russia as the world’s second global PGM supplier. In addition to PGM output, a by-product of this mining is nickel and copper extraction. In this application example the effectiveness of the separation process (gravity separation and hydro-separation) by comparison of PGM mineral content, both in concentrate and in tailings, is studied.
pdf – 2 MB
Exoscopy of quartz grains in SEM
Exoscopy (surface micromorphology) of quartz grains is one of the geomorphological methods used to determine the predominant type of sediment transport. Sediments can contain several genetically diverse types of quartz grains, for example with glacial, fluvial or aeolian features of transport. Grains of glacial origin usually show sharp edges. There are no signs of roundness or smoothing. Their surface can be either matt or glossy. Fluvial transport makes surface of the grain round. Typical is the presence of V-shaped pits. Grains of aeolian origin are more rounded to oval and usually have a matt surface. The genesis of sediments can be influenced by more than one factor; therefore grains can carry on theirsurface complex structural features. The most frequently, exoscopic research it is performed by means of scanning electron microscopy methods, because they allow users to identify any surface irregularities of clasts.
pdf – 1.6 MB