X-ray CT scan dataset of Darley Dale sandstone sample tts6. This sample was deformed in a true triaxial apparatus, and is fully described in the PhD thesis of Stuart (1992, UCL). The sample is a cube, measuring approximately 50 mm on a side. The sample experienced two sets of true triaxial deformation (test DDSS0009 and DDSS0010), with different applied stresses in the 1, 2 and 3 directions. This deformation produced distinct families of brittle microcracks, which were detected using acoustic emissions and seismic velocity analysis. This X-ray CT scan dataset was collected in 2019 at the University of Aberdeen by Dr Stewart Chalmers and Dr Dave Healy.