Petrography

Petrographic Analysis

Description and classification of rock thin-sections

The description and classification of rock samples in so called "thin-sections" is carried out with the aid of transmitted light microscopes under crossed-polarised and plane-polarised light. This analysis is indispensable in the classification of rocks and enables the determination of the depositional environment of sedimentary rocks, the description of the sedimentological and microtectonic structures as well as the assessment of the petrographic history of a rock (for example diagenetic alterations). The following is an example of a petrographic analysis of a sedimentary rock. In this case, the rock was first sawn into shape and embedded with blue epoxy resin. This method allows better visualisation of the pore space and furthermore image analysis methods can be carried out to quantify the microscopic pore space.

Figure 1: Overview of the production of a thin section specimen (left) and the image data of a thin-section recorded with a light microscope in plane-polarised (top right) and cross-polarised light (bottom right). This example shows a sedimentary rock consisting of spherical to elliptical ooids which have grown concentrically. The ooids are made of aragonite and were partially dissolved during diagenesis. The original pore space was cemented by calcite. The analysis of the pore space is important in this case, since such sedimentary rocks represent an important lithology for natural oil and gas reservoirs.

Applications

Petrographic analyses may be of interest to customers in the following industries:
  • Natural oil & gas industry: Characterisation of the rock fabric, the microstructures and quantification of the pore space
  • Mining companies: Holistic view of an ore rock and evaluation of the characteristics of an ore mineralisation
  • Natural stone industry: Classification of a natural stone, e.g. for the determination of potential substitutes for monuments
  • Renewable energy: Classification and characterisation of rocks for geothermal energy use
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