Many laboratory tests of samples where the rock fractures are based on meso-scale (cm) characterization of effective ‘intact’ strength parameters neglecting the microstructure effects. Understanding fracturing processes at micro-scale (mm) will require models with microstructure data. However, data is lacking on micro-scale. Stylolites are natural rock-rock interlocked interfaces which form by a localized dissolution process and their interface contains minerals and material different from that in the surrounding host rock. Microstructures such as stylolites influence the tensile stress behaviour in a rock formation. We are interested in stylolites because they can act as drains or as barriers to flow. Therefore, we introduce a study where we investigate on micro-scale failure mechanisms of limestone samples with stylolites in diverse orientations. In preceding study (Pluymakers et al., pers. comm.) a series of Brazilian Disc Tests was performed on eleven samples all including stylolites of microscale carbonate samples from the ”Treuchtlinger Marmor” formation from the Molasse Basin (Munich, Germany). All experiments were filmed using a DSLR camera. In this study we aim to develop the use of the Particle Image Velocimetry method to analyze such type of movies. We use the developed Particle Image Velocimetry method to analyze three of the movies of the preceding study, which contained samples where the stylolite is at different angles to the horizontal axis of the sample, so to s3. Two samples has an angle of 90° between the stylolite and s3 and one with an angle of 40°. In this open-source software the pixel displacement is analyzed in frames (i.e. consecutive images, ’before’ and ’after’ image) and it calculates the velocity distribution within the framepairs, but it is also used to derive, display and export multiple parameters of the flow pattern. In this study we derived and displayed the strain rate on the image pairs. The results show that the strain field of the two limestone samples of a 90° stylolite behaves identical in the two major stress drops (i.e. DStress) from the stress-displacement curve. However, the sample with a stylolite of 40° behaves differently. For the two 90° oriented stylolites random extension and compression takes place at the first highest negative stress drop and symmetric extension takes place at the second highest negative stress drop from the stress-displacement curve. However, for the 40° oriented stylolites asymmetric extension takes place at the first highest negative stress drop from the stress-displacement curve. And random extension at the second drop. Another result of this study is that the strain rate obtained from PIVlab, the strain rate per stress drop (MPa) (i.e. in the stress displacement-curve) in both the two 90 ° stylolite samples and the 40 ° sample were different. To put this work in the broader context of the energy transition, we consider the rapid development of the geothermal sector. Nowadays geothermal energy is considered as one of many alternative sources of energy using the hot water in the Earth’s surface to generate electricity and power heating/ cooling systems. The Dinantian carbonates in the Netherlands and the ”Treuchtlinger Marmor” carbonates from Germany are of interest for Ultra Deep Geothermal wells, because of their high geothermal potential. To enhance the porosity/permeability in a formation where hot water needs to be extracted hydraulic fracturing can be an option and this study gives insight about how the rock formations on micro-scale behave when tensile failure occurs. Tensile is one of the most important properties to be evaluated for any textile material (i.e. rocks). Tensile failure is important because it occurs when the stress on a component exceeds the strength of the material thus it determines the strength of a rock and consequently is influenced by single plane of weakness such as stylolites.