Integrating rotational components to optical properties observed in petrographic thin sections via automated image acquisition and analysis

The analysis of petrographic thin sections is a widely used process for the identification of the mineralogy of rocks and the analysis of their textural and microstructural characteristics. Despite the benefits of petrographic thin section analysis, it remains a time-consuming process with the results produced being subjective and relying on the interpretation of the researcher. In this study the benefits of integrating rotational data for petrographic thin section images in plane and cross polarised light to improve the outcomes of image analysis were investigated. This was done using image stacks representing a full 90° rotation of the thin section because the angle between the polarisation of light and the mineral crystal orientation alters the set of observed properties for each grain. Since the range of colour values upon rotation are more indicative than a single value at one orientation these are then attributed as ranges to each pixel. Grain segmentation is performed on these images and the pixel values are extracted and attributed to their associated grain. This is done with the assistance of Micro-fabric analyser (Visalli et al., 2021) a software developed to identify grain boundaries, and produces a dataset of objects representing their associated grains along with the corresponding shape data. Using the extracted pixel values, the aim is to determine a number of optical properties such as birefringence and extinction angle (both properties that rely on orientation of the mineral grains and therefore could not be extracted without integrating rotational data). These calculated values provide more diagnostic indicators of the minerals present as well as providing microtextural data for the minerals observed. Textural data for mineral groups are extracted such as grain shape, size and orientation. To achieve this, workflows were established for the acquisition and compositing of data to optimise the image analysis process. Image analysis can help with quantifying mineral properties and textures, but geologists still need to interpret these properties and textures. By improving the techniques used to train geologist, the better they can use these newly develop tools for thin section analysis. There are many techniques that can be used. One such technique includes using geoscience educational games to give geologist hands on experience with these minerals. Using educational games have been shown to be an effective strategy in a number of science fields, helping students retain information along with fostering peer to peer engagement. This paper introduces a new card game developed as a teaching tool for optical microscopy. The game includes 44 mineral cards with information on their optical properties. The game is designed to be easy to play to improve learning in students and to increase interest. The game was introduced to students at second- and third-year undergraduate level in a BSc Earth Sciences degree and was surveyed on their experience and learning metric were analysed, with survey data showing an increase in question scores after exposure to the game. Students also reported that they found the game an effective and useful tool while also finding it enjoyable to play.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Pretorius, Jacob Johannes

Advisor dc:contributor.advisor

• Mayne, Matthew Jason

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135924

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135924