With the recognition that the mineral talc is common in the cores of many exhumed faults, it has been suggested that talc may be important to the dynamics and modulation of slip in active fault zones. Talc’s wide stability field allows it to persist both at shallow depths and deep into subduction zones and experimental data suggest that it is also rheologically weak. To understand the behaviour of polycrystalline talc at conditions relevant to a subduction zone environment, we conducted a series of high-strain torsion experiments on natural talc at high pressure (1 GPa) and temperatures (450-500 °C). Scanning Transmission Electron Microscope (STEM) imaging revealed a marked decrease in grain size (long axes reduced from ~3-5 mm to